As an example of the 3pt% in HS meaning anything, I can offer these examples.
Robert Palmer DI (#32 SG coming in)
HS FG% 35.5 FG3% 38.7
21 games into his Senior year
career FG% 47.6 FG3% 42.0
Barry Allen DI (#95 SF coming in)
HS FG% 47.9 FG3% 34.3
21 games in SR year
career FG% 47.8 FG3% 40.0
Alvin Hale DI (#70 SG coming in)
HS FG% 35.1 FG3% 43.9
after SR year
career FG% 43.6 FG3% 41.6
With Palmer and Hale, I expected them to be good 3pt shooters because they shot better in HS. Neither really disappointed. They didn't shoot the 3 better overall, but they weren't too far off the rest of their FG%.
Allen wasn't expected to be much of a 3pt threat, but he is shooting 40% for his career thanks to high potential in per.
Now on the flip side, here's another that proves my point.
Leonard Carey DI (#57 PG coming in)
HS FG% 60.5 FG3% 36.6
Career FG% 51.7 FG3% 31.7
I didn't expect Carey to be that great at the 3 based on his HS stats, and he wasn't. 31.7 is okay, but 20% lower than the rest of his shots.
You might be able to get an idea of how they'll turn out, but you never can tell for sure. I thought this guy would be a great 3pt threat, but he never was.
David Gearheart DI (#5 PG coming in)
HS FG% 34.0 FG3% 43.3
Career FG% 45.6 FG3% 35.4
In most of those cases you can use the comparison between HS FG and FG3 %s to get some type of idea how they'll turn out, but the last one busts the theory.