I don't think a merely unsympathetic alien need be amoral or dishonest - they might have worked out a system of selfish ethics or a clan honor/obligation system. They'd need something to stop their society atomizing. They'd be nasty and merciless and exploitative, but it's possible you could shake appendages on a deal and trust them to fulfill it.

What would make a maximizer scary is that its prime directive completely bans sympathy or honor in the general case. If it's nice, it's lying. If you think you have a deal, it's lying. It might be lying well enough to build a valid sympathetic mind as a false face - it isn't reinforced by even its own pain. If you meet a maximizer, open fire in lieu of "hello".