When a paper is accepted to be published in an IEEE journal, the publishing system sends by email a PDF file of the author's version (for an example of what PDF file I'm referring to, see https://arxiv.org/ftp/arxiv/papers/1710/1710.01077.pdf).
(1) Is this PDF file the 'Accepted' version which can be uploaded to arXiv?
(2) Since in this case the authors do not have the source files of this PDF file, it is OK to bypass arXiv LaTeX detection?
How does IEEE define an “accepted” version? An accepted article is a version which has been revised by the author to incorporate review suggestions, and which has been accepted by IEEE for publication. If peer review by a journal or a conference requires no changes for publication, the accepted version is identical to the version initially submitted by the author. (Source)
From the link you posted, it is unclear if e.g. the copyright statements at the bottom were already present in the submitted version, but it is likely that the "author's version" is slightly different than the "accepted version". To be certain you are uploading the correct version, use the one you have compiled yourself. (That way, you also have the source files, solving question 2.)
\IEEEoverridecommandlockouts\IEEEpubid{\makebox[\columnwidth]{ <copyright statement here> \hfill} \hspace{\columnsep}\makebox[\columnwidth]{ }} placed before \begin{document}