Chinese dwarfs generally will live together. They will scrap occasionally but on the whole they're pretty social with each other. It could be boredom that's causing it, especially if you've only one wheel.
Syrians however will not tolerate another and need to be separated by 12 weeks old.
I've had 4 C/D hamsters in a cage together and they were fine and I even got them to the point where they'd hop on to my hand for a choc treat.
Aslo had a Syrian and he got to the point of tame that I rarely fastened his cage which was pretty big.
Cage:
Wedge:
https://dl.dropbox.com/u/43666878/wedgedesk.jpg
Syrians however will not tolerate another and need to be separated by 12 weeks old.
I've had 4 C/D hamsters in a cage together and they were fine and I even got them to the point where they'd hop on to my hand for a choc treat.
Aslo had a Syrian and he got to the point of tame that I rarely fastened his cage which was pretty big.
Cage:

Wedge:
https://dl.dropbox.com/u/43666878/wedgedesk.jpg