I use the mod for my modded SMP, and I've noticed that with the mod enabled, Forge will state "Incompatible FML Modded Server" next to the server ping. A standard client-side mod would flag itself as such to Forge and be safely ignored. This doesn't stop me from joining the server, just causes the warning.

An alternate solution to this issue would normally be to put it in the server's mods, but doing so causes a crash, which I'm sure is a known issue already.