I can't speak for other pools, but http://coinfu.io doesn't try to exploit the system by switching pools when a reward is due (however we do think this is a poor coin design). We also have implemented hashrate spreading to limit the hashrate going into a single coin. We try to mine multiple coins at a time if possible. Not only does it defeat the purpose of the multipool by crushing a small coin with a large hashrate, but the pool could potentially start orphaning it's own coins.