[Which thing? The vampire thing? The evil overlord thing? The fact that they don't even know where he is?]

Assuming most of his army is out conquering other worlds, the security surrounding him may be minimal. The biggest trouble would be locating him, as he could be hiding in literally any world. [But hey, let Benny know when you find him, pops. He may never get another chance to watch Edward Cullen get murdered.]