In terms of accepting yes, a three week old is still a baby so likely to be accepted by another hamster.
The issue here is the age of your female. Your female isn't an adult herself yet, but is able to fall pregnant, and your young male will very shortly be at the age he could impregnate her. I took in a robo that had got pregnant at seven weeks old and her poor little body was absolutely ravaged by what had happened, never to recover. The health of the hamsters, the female in particular must be your priority here, I don't breed my females till they are at the very least three and a half to four months old.
You also have the issue of ethical breeding here, I know nothing about your Campbells, but will assume they are both from healthy traceable lines, ansd therefore suitable for breeding?
