I have not run into any issues with Nicehash not paying out.  I've been mining cryptonight with them for about a week and have been getting payouts each morning to my Nicehash wallet.  I've cashed out once to my own btc wallet from Nicehash, again without any issues.  I will say that whattomine has always projected my earnings to be slightly higher than what they end up being, but this has been true with most coins I've mined and checked my projected profit through whattomine.  I'm guessing this could be from me not having my cards running at optimum levels or whattomine calculating slightly high.