im not at all concerned that he looks thin. I am concerned that if he has had surgery on his reproductive organs that his ability to breed may be compromised. Also, I am concerned that it might not be safe for him to breed.
If you can, why not contact the vet that did the procedure?
Looks like a mojave bumblebee.
I assume the breeder gave him to you because he was no longer capable of safe or reliable breeding. A multigene male like that is a valuable component of a breeding colony and would be hard to justify giving away for free otherwise.