I do not believe that a tow truck is "recreating" at Glamis and do not understand how they could be required to purchass a "Demo Fee" pass...
And someone who is supplying a service at the behest of someone else while at Glamis is not necessisairily a vendor. The burden of proof would have to be on the BLM.
(It is not REQUIRED to have a pass to drive around at Glamis on the public roads!!!) You can drive around all day and all night if you wish. You could even argue that driving along sand highway or other dune areas does not require a pass, though you would have to be careful to not be "recreating"... For instance... your 16year old is missing and you are looking for his vehicle.
Here are some interesting court cases...
http://www.freeourforests.org/adpass.htm#legal
Two different judges have ruled two different ways... (the second one ignoring the first) concerning the ticketing of empty vehicles.
The first judge says that the burden of proof is on the officer (as it should be) to witness the "recreating" and therefore he cannot ticket an unoccupied vehicle.
To date, according to the above webpage, there has never been a fine of over $75.
Many other interesting things on that page.