No, there is no game I know where someone in blockstun could be throw.. that would be pretty sick.. any frame advantage move would be a guaranteed throw setup^^
..and the only game where you can throw someone who is in hitstun is afaik KOF..
So in GG you can't be thrown while in hit- or blockstun.. but you can be thrown out of staggers or when you are in dizzy state.
Furthermore every move that is airborne is immune to groundthrows.
Considering air throws, you only can be thrown if your about the same height of your enemy or a higher.. If you're a certain amount lower than him, his throw won't connect.
..so the best positioning for an air throw is lower than your opponent, so you can throw him, but he can't throw you. You have to experiment a bit until you get the right positioning.
Furthermore some moves have throw invincibility on some frames, even that the chara is not airborne while doing it.. (for example the 6K of Order SOL [first 21 frames], or most DAAs)
And the first 7 frames after you got up from a knockdown, you can't be thrown.
Another thing to mention, is that some throws even have properties that only activate if they score a CH.. but the only way that a throw gets a CH is through a blinking guard gauge.. (try it with Robo Kys standard throw (6H) to see what I mean)
that's it about throw properties..