Do you join GAs of those you have blacklisted?

Nope. Doesn't seem fair, wouldn't feel right.

Now I might get tempted....but still. Nope. Course...I dont blacklist people unless I feel there's a really really good reason.

I wouldn't consciously enter.
I had the same problem you had in one of the giveaway groups im in. In the description i just said something like "if you have me blacklisted I would prefer if you didn't enter my giveaways, I understand if you don't want me entering public/private GAs but i don't think its fair that i can't enter your group giveaways" and im pretty sure i gave away a relatively good game that time :)
The next time the person made a group giveaway i realized I wasn't blacklisted anymore.

Doing it is damn rude. No and you should not be able to enter giveaways of the people you blacklisted.

I don't (+ they usually don't make gas)

I have 93 people on my blacklist and don't recall seeing a giveaway I wanted to enter that had the creator marked as blacklisted (and I'm using the Blacklist/Whitelist Indicator script). It seems they don't create many giveaways or the ones they do I'm not interested in. In short, I wouldn't enter such a giveaway knowingly, but in reality it's a moot point because it just doesn't happen.

No, never blacklisted/whitelisted anyone.

gif from the tv-show blacklist >

View attached image.

Hm... I don't think I ever saw a GA by any of the handful of people I have blacklisted...

This sums up my answer perfectly (ಥ_ಥ)