Yep, this is how I run the Ravens offense.
What I do is make Rice #1 HB. I set McGahee as the formation sub in some of the offset-I formations and use McClain for the tight-I formations (use the jumbo package) and make sure to call FB runs out of the other I formations.
I also try to use Rice in the passing game a lot. Raven Empty is a formation I like to use and sometimes use the formation sub the splits the HB out wide. Otherwise, I'll throw to him on swing routes and other out of the backfield routes (the light blue release routes) and the occasional slip screen.
I think it works pretty well. Like you, sometimes I notice one back having an awesome day. A lot of times, it's McGahee, especially if I lean on Rice a lot. I imagine that's mostly fresher legs in the 3rd/4th quarter against a tiring defense, especially if we've moved the ball well on the ground.
I haven't had 3 100-yd rushers, but I've had both Rice and McGahee with a high average and McClain with a decent one (and usually a TD). I've run the ball as much as 40-45 times with Rice and McGahee getting about 17 a piece and McClain the rest.
Works to eat the clock, even if it struggles, and I think it's a nice strategy for them.