Putting on my barracks lawyer hat: tipping for services such as baggage handling and food service while on a business trip is in the very definition of "meals and incidental expenses" (M&IE). Which is why you get non-taxable per diem under IRS rules as a transportation worker while on trips which overnight away from base. (Source: IRS and ALPA)

Hate to break it to you, but the guy driving the La Quinta van isn't getting retainer from your employer. Whether you tip the van driver or not is up to you, I guess, but the intent of your $1.95/hr, or $46.80/24 hr period, is to cover expenses on the road. It ain't difficult to carve out part of that per diem and be a professional.