Is there any risk in entering fake giveaways?

no, you are safe.

they can get your email address if you win, and they can get your steam profile if it's public. That's it, and that's the same as any other giveaway.

The only other risk is the disappointment of losing the points you used to enter, and which you got for free.

No. There is no risk at all

You lose points, that's it. Or maybe get frustrated if you win and not get the game.

Sometimes some ppl create fake giveaway intentionally to make ppl join some group, and then never giving the game to the winner. Other may do this to fool ppl into giving feedback to something they need and then never giving anything to the winners. But it's not really risky.

If you enter fake giveaways just from ppl who don't understand SG rules and think the game they give away will magically appear out of no where, then in that case there is nothing to worry about.

Well , first of all there is the risk that you waste all of your luck on them ... and never win a legit giveaway :)

Now with all seriousness , The only thing you lose is points ... since even if deleted you dont get them back .
Aside of that ... you dont lose anything .

By the way: were there any non-invite, non-group, sub level 5 GTA V giveaways that were actually legit? So sort of actually public legit giveaways?

You might win.

Except for the points you can only lose something, if someone add you, and he get's you to visit a phishing site or so on, but this coud happen everywhere, and if you just think a litle bit about what you do, you'll be fine.

Ebola.

Yes, you will lose all your points (if you win or if it is deleted) because the refund system still doesn't work as intended.
EDIT: Also be careful around people who tend to sloppily delete duplicate giveaways without warning, as even unintentionally, any deletes refund no points.
Which also creates the unfortunate side effect that users have to judge by themselves whether a giveaway is reasonably legit before entering it, as opposed to being able to freely enter everything and have site+admins sort things out in the end.

Well, I would be sad if I would win GTA V and then actually not get the game because the creator didn't read the faq or used its brain. It's just a huge disappointment (even with smaller games), so that's the only "danger" there is.