I've been around bounties for only a short time, and it looks like they all pay in their native tokens. However, I've seen dice sites pay high ranking members either per post or weekly, and these were in ether or bitcoin, not tokens. The ones I've seen only had a few spots, for very high ranking members and these were established sites, like cryptogames and a few others. I've also seen a signature club where there is a small group of high level members, and you pay them fixed amount (each person had their own rate) to carry your signature, it wasn't cheap. I've also seen members renting their signature, and they wanted established coin for it, not tokens.