I've been having a play with ethereum mining @nicehash just to see if I can get it to work. The conclusion is that it's seriously messed up - not sure if I could trust my hash there.
Firstly the statistics reporting seems to be broken - I had immature and unexchanged coins on there but now they only show on the graph and not anywhere else. Looks like I mined for nothing.
Secondly I had another play today and pointed my rig at it again. So far, even though shares are being submitted, it doesn't seem to display any information at all - 0's across the board. This could be just that the reporting is broken atm (explaining the above too).
Lastly there seems to be a (relatively) huge delay when submitting and this caused one of the cards to cr*p out a couple of times. The GPU utilisation also drops considerably (other pools you see a drop of 2-3% on submit but for Nicehash it's up to 50%).
Maybe it's all just a reporting glitch but it doesn't inspire confidence.. I assume that it's currently just running as a pool (and maybe it's hard to integrate that into the infrastructure which is based on selling hash) so hopefully at some point you will be able to sell ethereum hash?
Would be nice to have some official comments @nicehash You know we want to like you here!