This question has been asked too many times.
If you read the EULA, you'd notice -- if you play the emulator it is considered illegal.
But the chances of them actually doing anything against you for playing EQEMu are low. If anything EQEMu supports EverQuest. If it wasn't for EQEMu, I wouldn't be playing EverQuest at all.
If you don't go screaming out all your info to your personal account, and give out your account info. Your pretty much safe.