Wolfhawk has:
We've been having friendly arguments about this power. Some of my friends think it overrides the rules that stops you activation the same game effect more than once a turn, and others say that she has to target a different character each time she uses incapacitate in order for them to be different actions.

Legolas has:
There was a game the yesterday where I had Legolas charge Alfred, and KO'd him, then charge a GCPD motorcycle and KO'd that too, and then charged a Red She-Hulk. It didn't occur to me that using Charge more than once like this might be illegal till I was trying to figure out Wolfhawk's power. So am I right in thinking that he can he only get a free charge once a turn?

It's telling you that you can do it otherwise. Otherwise, whats the point of the power? It also never says that he must target a different character. Only that he can use incap as a free action so many times.

Yes. In this scenario it never says that he can keep using it or use it so many times for whatever reason. So he would be limited by same effect rule.