[@Dead Cruiser]

I do agree with that logic, but I see it as something else (kind of):

The Enclave are using the slavers as a way to familiarize themselves with the wasteland from a wastelander's view. Since I'm guessing they don't feel like sending out masses of troops or vertiberd recons to scout the wasteland out. Second, they may not recruit the slavers or their slaves, but they can be used as meat shields preventing their actual worthy soldiers from taking all too much damage. And because the slavers are so poor, the Enclave wouldn't need much on bribing them to be said bullet sponges. If a degenerate gets killed, boo hoo roll the next one in, but if one of their men get killed, things get problematic since they just lost a trained guy and all of his equipment.

Of course, this is all from a war point of view tho.