Well it is obviously going to be a problem for the mechanics if there is no drivers seat - it is going to make it impossible to test drive, and nearly impossible to even move it into the service bay without something for the mechanic to sit on...
In my van, it is possible to move the passenger seat into the drivers seat position, would that be possible in your van?
If not is there some other alternative you could provide, even if it's something as crude as a folding beach chair? (or do you have a backup chair you could let him use?)
A second possible issue is the controls... In my van, the normal AB controls are still there, and work normally, but in a lot of vehicles with more "high-tech" adaptive gear, they might not be, or the mechanic might need to change things to make it possible for him to drive the car...
It might be helpful for you to talk with the service manager and / or mechanics to see what they would like to do - perhaps it would be easier if you offered to stay while the car was being worked on so that you could get it in and out of the service bays, do any test drives, and so on...
It will help if you do your best to sound mechanically clueful so they will be inclined to bend any rules against customers in the service areas (as opposed to being one of the persons that CAUSED those rules...
)
I haven't really had my van long enough to need much service, but the only issue that I've encountered so far is that because of the lowered floor I have had several places say they can't work on the car because I won't fit over their lifts...
ex-Gooserider