I would think hunters would be awsome in BG but not that awsome in Arena.
they are a ranged class and don't do well when people get into their face.
I used to LOVE my 4x hunters/shaman at level 70 in AV and have 4x boars ( all named spam ) squeeling as the run for a target, I must have laughed for 10 minutes the first AV I did with them.
I never tried my hunters in Arena though and they have been collecting dust since WoLK came out.
I have no desire to PvP, there isn't any gear I need from there and the AoE is so devistating these days that anyone clumped together gets wacked fast.