pblais wrote: I have seen where one user has used the Roland UM MK2 but has not had good results with Hauptwerk recognizing it and whatever device is connected to it.
I think you might be referring to this post: viewtopic.php?f=3&t=16117&p=121086#p121086 .
If so, that wasn't actually any fault or compatibility issue -- the problem was simply that its owner hadn't installed the driver for his Roland UM. I don't think I'm aware of any reasons not to use a Roland UM Mk2 (although I don't have one myself). Roland's products are usually good-quality, so I would expect it to be a perfectly valid choice.