First, as already noted by the_traveler, you'll never find an engineer in this car unless he/she is on vacation and taking an Amtrak train to get there. And while the conductors hang out in this car to do their paperwork, they too should never be asleep in this car and are not assigned a room.These is basically the "Crew Car" where the engineers, conductors, service attendants, chefs, cafe car host, ect, ect sleep when not on duty. It's also considered to be the "Overflow" car when everything else is booked out but there is still a demand for rooms. They usually only have two of these rooms available at any given time for paying passengers. Also, there is no car attendant. If you need assistance, you will have to go to the next car over and deal with that car attendant.
Next, typically at least 4 rooms are sold in this car and on some trains up to six can be sold if other/non-crew Amtrak people haven't booked the rooms.
Finally, while there is no dedicated attendant strictly for that car, either a coach attendant or a sleeping car attendant for one of the other sleepers is assigned to take care of the revenue passengers in the Trans/Dorm car.