The other answers are both correct, but I'll try to clarify further. The quoted sections are from the GPLv3 text.
In the text of the license, interpret "you" to refer to the person/company which sold you the system including the software; the license is talking about the terms of what they can/have to do with the software, including what they have to do if they distribute it.
"Considering this is an embedded system and no software/binary is physically handed over" - Acccording to your description, the software is absolutely "handed over", it's just handed over on a SD card. But GPLv3 uses more specific terms for this:
To “propagate” a work means to do anything with it that, without
permission, would make you directly or secondarily liable for
infringement under applicable copyright law, except executing it on a
computer or modifying a private copy. Propagation includes copying,
distribution (with or without modification), making available to the
public, and in some countries other activities as well.
To “convey” a work means any kind of propagation that enables other
parties to make or receive copies.
In this sense if you purchase a physical product with binary of a software on an SD card, it is both "propagated" and "conveyed" to you by the seller.
"does their code which integrates with the GPL licensed projects also need to be GPL licensed and their source made available to the users" - Yes, it does, because of this part of GPLv3
You may convey a covered work in object code form under the terms of
sections 4 and 5, provided that you also convey the machine-readable
Corresponding Source under the terms of this License, in one of these
ways
(followed by a description of different ways of providing the source code)
This means that the object code can only be conveyed if the source code is also conveyed using one of the described ways. Without that, they don't have permission convey the object code - including, in particular, they don't have permission to sell you a device with the object code in it.
However, the specific meaning of "integrates with" needs to be handled carefully.
To “modify” a work means to copy from or adapt all or part of the work
in a fashion requiring copyright permission, other than the making of
an exact copy. The resulting work is called a “modified version” of
the earlier work or a work “based on” the earlier work.
A “covered work” means either the unmodified Program or a work based
on the Program.
You may convey a work based on the Program ... provided that you also
meet all of these conditions: c) You must license the entire work, as
a whole, under this License to anyone who comes into possession of a
copy. This License will therefore apply, along with any applicable
section 7 additional terms, to the whole of the work, and all its
parts, regardless of how they are packaged.
A compilation of a covered work with other separate and independent
works, which are not by their nature extensions of the covered work,
and which are not combined with it such as to form a larger program,
in or on a volume of a storage or distribution medium, is called an
“aggregate” if the compilation and its resulting copyright are not
used to limit the access or legal rights of the compilation's users
beyond what the individual works permit.
So the key question is whether the software which integrates with the GPL software together forms a "work based on" or an "aggregate". This depends mainly on how the two interact, and whether they are "separate and independent". By its nature, including C/C++ headers in C/C++ code usually creates a "work based on" because copies of parts of the headers end up in the object code. Calling a command line program is usually an aggregate. Simply importing a python module in python code is less clear; I don't think I can reliably tell you whether that is a "work based on" or aggregate. But if it is an obfuscated binary that needs to be run through a decompiler to see the python code, that (as a whole) is almost certainly a modified work as well. If it is importing a module which is essential for function rather than optional, it is probably also a modified work.
Lastly, there is the issue that @hlieberman brought up: is the device you purchased a "User Product"?
A “User Product” is either (1) a “consumer product”, which means any
tangible personal property which is normally used for personal,
family, or household purposes, or (2) anything designed or sold for
incorporation into a dwelling. In determining whether a product is a
consumer product, doubtful cases shall be resolved in favor of
coverage. For a particular product received by a particular user,
“normally used” refers to a typical or common use of that class of
product, regardless of the status of the particular user or of the way
in which the particular user actually uses, or expects or is expected
to use, the product. A product is a consumer product regardless of
whether the product has substantial commercial, industrial or
non-consumer uses, unless such uses represent the only significant
mode of use of the product.
This actually has no impact on whether the seller has to give you a copy of the source code; they would have to whether the device is a "user product" or not. But if it is a user product, they also have to give you "installation information", ie everything you need to load your own (possibly modified) copy of the software onto the device:
“Installation Information” for a User Product means any methods,
procedures, authorization keys, or other information required to
install and execute modified versions of a covered work in that User
Product from a modified version of its Corresponding Source. The
information must suffice to ensure that the continued functioning of
the modified object code is in no case prevented or interfered with
solely because modification has been made.
I think that about covers the terms of the GPLv3 as they apply in your case. If you suspect a GPLv3 violation (and clearly having obfuscated code suggests that it is a knowing violation), I would encourage you to contact the authors of the software and the FSF, and let them decide how they want to handle this. There have been some prominent cases of big companies losing GPL cases against the FSF; it wouldn't be bad to add one more to the list.
