I read an article on the Chrysler TPMS and it stated that if a Chrysler mechanic took of your tire and the TPMS light was on then legally he cannot let you drive the car away as he is liable.

Before attempting to replace a Chrysler TPMS we advise the use of one our Bartec Wheelrite tools to establish the need for replacement and the nature of the fault. This may support a warranty claim but will also ensure that the dealer or tire shop is covered for liability claims. The legal position is that as soon as the dealer breaks down the wheel then he becomes liable and cannot allow the car to be driven away from his shop with the TPMS warning light still on. Many dealers have found that customers will not accept the costs for repair and may attribute any breakage to the dealer if there is no audit trail.

So it would appear that if your light is on do not take it to a dealer for tire dismounting as he will get you to pay for new sensors before you can drive away.
I suppose that if you and they agree before hand that it is not working and you want the work done then you are probably OK ... maybe.
The full article is here.
http://www.chryslertpms.com/

Edit, wrongly attributed, thanks Max.