Hi, Scott. You certainly can do what you wish, but I agree with your contractor. However, I don't think that the problem is as much the hollow core doors as it is the hardware that just does not hold up. It's not real comforting to know that sometime within the next 20 years you will have to tear open a wall to replace the sliding hardware.
Older houses that had solid core pocket doors also had heavy hardware to go with them. This may be why your contractor feels that the answer is the solid core doors. But I don't think you can buy comparable hardware today. The thin sheet metal stampings and plastic or nylon parts just don't hold up as well as the heavy steel parts used on the old doors.
Certainly, this is my opinion and other's $.02 worth might be different. Henry in MI