After seeing their draft grades, I think all 3 were probably coming back anyway. Still, this can't hurt.
I still believe that Kamara will go ahead and enter the draft. The shelf life of a running back in the NFL is so short, plus he's not likely to increase his draft position considerably by coming back and splitting time with Hurd another year. And add to it that he has been at 3 different schools in 3 years, so he's not likely to be anywhere near in credit hours where he needs to be to graduate in 4 years, so that's not likely a factor.
Of the 3, I still see him as the one most likely to go.