My Gary Fisher hardtail came with a deore rear derailleur on an 8 speed. I know the Deore 591 is 8 speed compatible and a bit nicer than the Alivio, Altus or Acera.
Check it out-
Also if I’m not mistaken the derailleur is just a dumb component anyway. The shifters are what determine how much travel there is when shifting between gears. Eg. a 9 speed shifter will move the derailleur in smaller increments than an 8 speed shifter. I would think that any rear derailleur would work as long as you have the proper shifters. Someone with more experience can verify though.