Unfortunately, Tsu is not safe. You still get a lot of spammers looking to make money (I had to block friend requests entirely because I kept getting requests from spammers). And you still get a lot of people who JUST DON'T GET IT. People who think Tsu is just like FB (in that you can post whatever you found on google!) except $$$. Tsu's reporting system isn't that great, either, which makes it worse.
Tsu requires $100+ in your account before they pay you, and it seems they actually check your account before paying you. And if they find out you're just reposting stuff you found, then they won't pay you. That's a good thing, and also logical because even if they don't care about respecting creators, of COURSE they care about where their money is going, right? I just wish they weren't so bad at dealing with copyright violations outside of the pre-payment account check.
Their invite system is really loose. You don't need a personally generated code; each account gets one invite URL, which can be used by anyone who acquires that URL. It can be reused again and again and again by multiple people. So it's not much of a protection, just a part of their whole "family" feature (which I actually kind of dislike, but eh, not a big deal).
Still, give it a try, though! There's a lot I like about the site. Just be sure to find other illustrators so you don't end up too isolated.
As for dA groups, they're entirely user-run. Anyone can make them. You can, too. The group founder can set out some rules about what kind of art to accept or reject, which they can enforce either alone, or with the help of a few group admins (fellow users they choose to trust). I don't get your question about commenting, though?
