Well, let me take a crack at it. As we all know, in the Vampire statblock, it explicitly says that vampires are always evil. Granted, we know that Rich isn't the biggest fan of the alignments that come included in the statblock, but the one explicit exception he spelled out was "leave inborn alignment to the overtly supernatural - if it exists at all - and away from the biological creatures". I'm pretty sure the vampires qualify as "overtly supernatural". Undead, at least from what we've seen in the comic, really are always evil. Even when Haley and Belkar are theorizing about Roy coming back as undead, they assume he's going to be evil, even if he is free willed. And why not? They're hollow mockeries of life animated by dark and terrible energies too horrible to imagine. For those reasons, I think we're actually safe taking the statblock's word on this matter, and Malack should be treated as Evil unless proven otherwise, nevermind the fact that virtually all of the circumstantial evidence corroborates the assertion that he's evil.