And since you wind up paying an exchange fee anyhow (mined coins -> BTC -> Payment coin) I personally recommend just taking BTC and exchanging it yourself. This way you can control the timing better (worse case its a wash as your paying the exchange fee either way)
Suppose you mine ETH and want to be paid in XMR, the pool will change to BTC before changing to XMR!?
If you want to mine ETH and get paid in XMR you are double hosed. They don't mine ETH or XMR. The only coins you can get paid in are ones that they mine and since they don't mine XMR you are sol.