Indeed, both are aliens and both are predators. XD And yet it works because they both have their own unique things about themselves.
Also, seeing as Hirogen and Predators both like hunting dangerous things, they might actually start trying to hunt each other. There can only be one Apex Predator!
Yes, them fighting Klingons would be a dream come true for both races. A Borg Predator would be cool to see. I think they'd give the Borg some trouble seeing as how most of their weaponry is physical rather than energy based. Maybe the Borg adapt to a plasma shot after it's fired a few times, but then they'd be faced with spear guns, actual thrown spears or shot wristblades, and not to mention in melee combat the Predator weaponry may have better reach than the Borg drones.
It'd be a great crossover with tons of potential.