They could be discoid, death's head, or B. giganteus. Most likely discoids though.
They aren't 'nasties' but in fact would be good for you to start a new colony with aside from your dubias. They reproduce a little bit slower than dubia, but still pretty quick.
I have three colonies going of different roaches, which allows one colony to take a break while I feed from the other two, and I just cycle them this way. I never run out of roaches since I started doing this.