Dennis, I have literally swapped a few hundred blower/AHU/FCU with non OEM replacements and had very few problems. As long as frame, RPM, shaft, rotation, etc are okay-I would not sweat it-pun intended.
Sizing a motor according to weight or amperage, as those clerks did, is just wrong and weird.
How many millions of cars, lawn and garden equipment, and appliances have aftermarket parts put in them? Some aftermarket parts are better or safer than the OEM they replaced. Just think how wrong it is for auto body shops to to some of what they do unless they replace damaged things with OEM components.
Warranties and listing .. understandable while warranty is still valid, unless you are authorized to do warranty repairs chances are you are not working on it anyway.