The Legion would probably hire Talon company and once they take Hoover Dam Talon company would be integrated into the Legion.

They destroy all markets and prevent development of strength, that and they would definatly go to war with Lyons Brotherhood, and Talon Company, while an enemy of the BoS, isnt stupid enough to go into direct war with them.
and what i am trying to tell you is that, unlike the Khans, the Legion wouldnt even approach them, they are everything the Legion hated about the NCR but even moreso.

@Jayrad, the Talon Company isnt a tribe, they work on capitalist values with guns, they wouldnt assimilate into being a bunch of slaves.

Reilly's Rangers are only four people, so if they say no it wouldn't be hard at all to get rid of them.