I would be willing to allow the presence of the filthy xenos if we could together crush an overwhelming force of heretical chaos, but as soon as they have been crushed by the wrath of the Emperor you shall be swiftly following them.
I was mere contributing an idea! But i anyway prefer range over melee, that is when the Heavy Bolter, Laser Cannon and Plasma Cannon is most efficient, especially against a whole bunch of... ORKS! Like here everywhere seem to run around!
I would be totally for fighting alongside Orks, at least once. Just so i can join the WAAAGH as a Space Marine, would be a funny sight. I'd probably kill them afterwards though.. No hard feelings, Greenskin. =p