I speak from pure speculation here, based on my understanding of things -- I've never used satellite internet myself.
I would expect it to be rather frustrating. Satellite has exceedingly high latency: often a whole second or more (that's about 100 times slower than cable or DSL, and 10 times slower than a 56K modem). So it won't feel "natural", which is one of the things that normally sets iChat AV apart (on low-latency broadband, iChat AV has very low latency).
You know how on TV news they have reporters all over the globe, live via satellite? Notice how they have to leave a pause after talking for the person on the other end to respond? That's the latency at work.
So I would say that it would probably work, but would feel very unnatural -- don't expect it to "feel" like a phone call.
tooki