I'm aware that some of the small (or outdated) ETH pools are not compatible with NiceHash.
Meaning - buyers of hashing power can't direct their bought hashing power to the pool they want to mine on. This could be due to poor coding skills or not being aware that NiceHash exists.
Now, I'm interested which are your top pools for ETH mining? So we can review their compatibility, because we don't want to limit your choices when buying hashing power on NiceHash. You should be able to mine on any pool you want!
If you are a pool owner, you can also visit this page directly https://www.nicehash.com/?p=pool-operators
to find more about the benefits and compatibility.