It's an interesting thought, and indeed there were Dwarves that fought alongside the orcs of Sauron. However, this would have been motivated through greed. There were some dwarves, such as those of Durin, that refused to fight for Sauron out of principle, or loyalty to the west, or because of past treachories by Sauron, but there were dwarves that were less scrupulous and much more driven by greed.

So I think you should look at it from that perspective. If the dwarves were driven by greed and the lust for gold, then I think that be very similar to other dwarves. I don't think they would be less or more mobile, but I can imagine they might fashion other types of weapons of war, such a crossbows. They are master craftsmen after all. I don't think they would use evil magic, but I also think they wouldn't say no to having an orc shaman or two with them to protect them long enough so that they can collect on their gold payment.

I think that's how you'd have to think about an evil dwarf faction. They're motivated by greed and will fight for the highest bidder for the lowest cost. Some of them might have heavy dwarven armour, some might have light dwarven armour. Some might have bows, some might have crossbows. Very much a mercenary company rather than full on evil.

At least that's my thoughts on the subject. So feel free to discard as necessary