Being an Opeth fan myself, I gotta say that there's a lot of cool fans out there, but just as many elitist jackasses. Generally the Opeth fans that like other legitimate (i.e. not on Headbangers Ball) metal bands act pretty much the same as the average AA or Orphaned Land or any other metal band fan. The fans that give Opeth fans a bad name are either the old elitists that refuse to like anything besides Opeth, or the teenage fans that think Deliverance is the only album Opeth ever made.
So what's my point? I guess if you find a fan of Opeth thats also into good but less known metal like AA then they're probably gonna be just like any other metal fan, so don't let someone being an Opeth fan make you immediately hate them.