I believe that my old company had something similar ("vehicle service technician" (VST)). Essentially, their job was to restock the units and do minor cleaning. They weren't EMT-Basics, so I don't think they knew what they were doing half the time (e.g. I found an adult BVM with ped mask one time. Another time I found an opened OB kit.). All of this was done with the idea that VSTs stocking units could decrease check out time in the morning (fully stocked cabinets were sealed in a manner similar to crash carts in hospitals) so it seemed that there was more scrutiny on the crews getting out than on ensuring that the units were properly stocked.
Personally, I see two downsides to programs like this. First, it is really easy for crews to notice a handful of mistakes and write off a VST style program. Once the crews lose faith that the service techs can do their job properly, any time saved is lost. Second, unlike the hospital, ambulances do not have backup. There isn't a monitor on the next floor or a Pyxis machine to draw extra medications out of if the pharmacy or stock room people make a mistake. That little detail makes a big difference between knowing that everything should be there because of a tag and knowing everything is in there because the crew checked.
As far as the company I worked for, the hours were at night (6pm-midnight ish). None of them were EMT-Bs because they would be working as an EMT-B if they were one (So. California ambulance companies are generally short of people). I'm not sure of the pay, but I'm sure that there were unpaid ridealong oppertunities if one of the VSTs really wanted to.
