no, they do not have to reimburse him. If it is a job related expense, he can take the mileage as a deduction on his taxes.
the one thing I am not clear on is: is he required to drive as part of his employment or is it simply that he is required to go to these other shops to do his job.
and just a note:
25-50 miles, one way (you did state 50 and 100 miles per day so I presume you were speaking of round trip) is not an excessive distance for one to drive. I currently drive 28 miles one way and have been required to drive 52 miles one way. If I did not want to drive, I could always refuse the work, just as your husband can.

