In my building if you go to do driver helper, you get your normal hourly rate while doing driver helper. HOWEVER, you will not get overtime until after 8 hours (instead of the normal 5 for PTers). I did driver helper a few times last year until I realized double-shifting would get me more $$ (and it's easier work than running up to houses a few hours a day!)
Driver helper is a great experience for those thinking about doing driving, though. I have a lot more respect for drivers after seeing how they have to conduct their days, getting to know their customers and certain requirements some have. One driver I helped had access codes to a lot of condo buildings (all of which were memorized), and also had keyless gate access to some other places as well. I delivered to an NFL player's condo, and he had a special access code set up for that driver. I thought that was pretty cool. Another driver didn't really even bother knowing addresses -- he read names and knew exactly where they lived (this was a mostly resi route). One customer received a lot of CODs, so he had it worked out that the COD checks would always be under the door mat. Both of these guys were 20+ year vets, so I guess after that much time you gain that knowledge. Overall, though, I'd recommend doing it at least a few times just to see what being a driver is like (or at least getting a small taste of it).