I think this is the relevant section of 2009 UPC:
This doesn't seem to disallow it, but I still seem to recall reading somewhere the UPC disallows wet venting into vertical drainage. Maybe 2012 UPC has some changes on this?908.1 Vertical Wet Venting.
908.1.1 Where Permitted. Wet venting is limited to vertical drainage piping receiving the discharge from the trap arm of one (1) and two (2) fixture unit fixtures that also serves as a vent not exceeding four (4) fixtures. Wet-vented fixtures shall be within the same story; provided, further, that fixtures with a continuous vent discharging into a wet vent shall be within the same as the wet-vented fixtures. No wet vent shall exceed six (6) feet (1,829 mm) in developed length.