Combinations of 150/1s and Pacers with wither their own or another class are running round all day. I am unable to offer and comments on Revenue Protection.
It can vary with Northern Rail. Some services have an additional person on board to check/sell tickets on the front unit, others don't.
What happens when there isn't an additional person varies as well. Sometimes the rear unit is only opened for part of the journey. Other times it's open for the full journey. The former has the disadvantage of a delay part way through the journey while the rear unit is unlocked or locked up and passengers are told to move to the front unit. The latter has the disadvantage of less passengers being asked for tickets.
With Northern there are also some out-of-use units attached to in service units in lieu of an
ECS▸ move. For instance, the 14:25 Buxton to Manchester is a 156+150+150. The 156 is used for the passengers, the two 150s on the rear are just there to get units back to Manchester Piccadilly in time for the evening peak. In the event of there being a special event on meaning the 156 is packed the guard could open the middle 150 as well. On the other hand the 16:51 Manchester Piccadilly to Buxton is 2x150s, both of these are used for passengers and the service is full and standing with a pair of 150s.