yes they do mine different coins concurrently, atleast amsterdam/useast/main are all on different sets. I would assume that the shares come from overall btc revenue and not from the specific coins themselves, so btc/mhs should be the same no matter where you're pointed.

all i know is i never received lost (counted as stale by cgwatcher) until the past 3 days and my reject has gone up (but the rejects are stale shares 99% of the time, as in stale share is detected and then it gets rejected and counts towards my reject instead of stale)

Today is a sad panda kind of day lol. If anyone is trying to tweak settings, today is the day lol