I have not merged mined with a ASIC, but I have merged mined with a GPU at MinerGate. At MinerGate you can merge mine with XMR with XDN or FCN. Merge mining lets you mine to a combined pool to mine a 2nd coin without the loss of any hashing power.
Thanks. That's what I thought it was. But I am trying to figure out if that is doable with S9?
There are a number of pools that support merged mining between BTC and NMC.
That combination was popular in the days of GPU mining SHA256 coins, but I don't know about now. (I never jumped on the ASIC train.)