Noticed this bringing an 86 shaman to buff for Brawlers guild.
Sucessful fights in the brawler's arena do give exp to anyone in that player's group. It's only 9000ish but you do get awarded it just for being in the group of the winning fighter and being present in the arena zone. This allows you to join a large buff group and simply AFK for a slow, but steady stream of exp. It also appears that the guild battle standard also increases this exp.
I haven't been able to determine at what level you can start benefitting from this, but it's definitely working 85-89.