Light truck tires are balanced (or should be). An unbalanced tire/wheel in a motorhome is every bit as unwanted in a motorhome as in a car.
At least around here, most tire shops wouldn't do an alignment by default, and many don't do alignments at all (especially for large vehicles like motorhomes). If the handling was acceptable with the old tires and they weren't wearing excessively or in an uneven manner, I wouldn't worry about the alignment; there's no reason to suspect it's incorrect. If, on the other hand, you have alignment-related issues, then doing the alignment regardless of whether new tires are needed or not seems to me to make sense.