Yeah ... they're not the same thing.

SMOS is a linux distribution that has been modified with all the miners you need preinstalled.  It has also been modified to have the ability to control it via the simple mining website.

Nicehash is an app for windows that switches from different mining algorithms in order to give you the best profitability for your hardware.  Then they pay out in Bitcoin, and I believe Bitcoin Cash.

In my opinion they are not really related.  Nicehash can be hacked because they store the hash keys for payouts etc. ... but Simple Mining can be hacked too, but just not really likely to be able to steal already mined coins.  Hope this helps.

Also check out HiveOS.  I'm going to be installing it soon.