I don't see the big deal - as long as MSU is not playing UM and their success or failure will not affect UM's season, I don't see the big deal about rooting for MSU. I'm not saying anyone should out of some "conference loyalty", but I really liked that Spartan team that won the NC and I was happy they won. I'm not going to run around with a faux Spartan war helmet on and paint my body green, but I wouldn't be unhappy if then won the NC. Same goes for OSU.
I think there is a fine line between team loyalty and pettiness. I expect MSU fans to cheer for UM losing as much as when they win, but I hope that the average UM fan is a bit better than that.