What is the gear rating for in the sniper arena?

Basically your shield rating. Higher Gear Rating=More hits needed to kill you

The higher the gear ranking, the more it takes to kill you. I know the previous comment says it means nothing, but I notice that I'm killed less in pvp now that my gr has gotten higher. So yes.......someone whose gun has been significantly upgraded may be able to kill you just as easily, even if their gear rating is lower.