Dealer still says problem is having a short serpentine belt vs long belt. Says that Saab did this to save money - doesn't make complete sense to me. They say mounts are all okay. I recently had transmission mount replaced (it was bad) but had no effect on vibration. Guess I can pay for new long belt (idler arm to accommodate long belt is installed) and see what happens.
Usually when one motor mount gets really bad, it puts undo stress on the other ones, and they fail soon after. On transverse engine mounted, front wheel drive cars, transmission mounts are the same as engine mounts.
A bad misfire or running condition would cause similar vibration or shake, but you would probably have a check engine light to show for it.
The belt alone is not a viable answer. Has the car always vibrated with this belt on?
Has the dealer plugged into the car to verify anything yet? First thing I'd check is vacuum at idle. What rpm is it idling at? Is it missing? I'd do good a visual once over on all hoses/connections and look for breaks