Here is a solution using complex numbers, i was waiting for the bounty to be given, myself having no simple synthetic solution.
I am still posting it, since there was an interesting experience of computing in the cyclotomic field $\Bbb Q(\zeta_{20})$.
Let $z=\zeta_{20}=\cos\frac{2\pi}{20}+i\cos\frac{2\pi}{20}$ be this primitive root of order $20$, a root of the cyclotomic polynomial $\Phi_{20}=Z^8-Z^6+Z^4-Z^2+1$.
We identify the vertices $A,B,\dots,T$ of the given $20$-gon with their affixes $a, b, \dots,t$ which are of the shape $z^k\in \Bbb C$, $k\in\Bbb Z/20$, so that $a=1$, $b=z$, $c=z^2$, and so on.
Then $V$ is the orthocenter of $\Delta JRE$, and the centroid is between zero and $V$ at one third from zero, so
$v=3\cdot\frac 13(j+r+e)=z^9+z^{17}+z^4 = z^4+z^9-z^7$. (Or use the parallelogram $VEHJ$.)
Then $U$ is the incenter of the right, isosceles $\Delta TLB$, it can be obtained as a $+90^\circ$-rotation of $B$ around $A$, so $u = 1 + z^5(z-1)$.
Then $U,V,H$ are collinear, iff the fraction $(u-h)/(v-h)$ is real, so iff the product $(u-h)(\bar v - \bar h)$ is invariated by complex conjugation. Now we compute:
$$
\begin{aligned}
(u-h)
&=(z^6-z^5+1-z^7)=(z^6+1)-z^5(z^2+1)\\
&=(z^2+1)(z^4-z^2+1-z^5)=-(z^2+1)(z-1)(z^4+z+1)
\\[2mm]
(\bar v-\bar h)
&=\overline{z^9 - 2z^7 + z^4}
=z^5(z-1)(z^5+1)(z^3-z-1)\ ,
\\[2mm]
(u-h)(\bar v-\bar h)
&=-z^5\cdot (z-1)^2\cdot (z^2+1)\cdot (z^5+1)
\cdot \underbrace{(z^3-z-1)(z^4+z+1)}_{=-\frac 1z(z^3+z^2+z+1)}\\
&= z^4\cdot (z-1)\cdot (z^2+1)\cdot (z^5+1)\cdot (z^4-1)
\ ,
\end{aligned}
$$
and the last expression is real, i.e. invariated by complex conjugation, because for $z^k\ne -1$
$$
\frac{1+z^k}{\overline{1+z^k}}=z^k\text{ , so }
\frac{\ z -1\ }{\overline{z-1}}=-z\ ,\
\frac{\ z^2+1\ }{\overline{z^2+1}}=z^2\ ,\
\frac{\ z^5+1\ }{\overline{z^5+1}}=z^5\ ,\
\frac{\ z^4-1\ }{\overline{z^4-1}}=-z^4\ .
$$
$\square$