Bet you never saw this, and I never thought I would either! (On my blog, the video is at the bottom of the page.)
Here's a video of all 4 hamsters playing together! Pip (robo), Pluto (robo), Smokey (Siberian) and Bear (siberian) all in a playpen together. I supervise them the whole time of course, so no fights come up. But I like for Pip and Pluto, who live alone, to have some hamster social time, to make their life a little more fun!