Touchfour - The direct answer to your question is yes. A similar scenario was discussed here recently. Technically he could sign with a NCAA, NAIA, and a JUCO. While unusual circumstances can happen, I just never feel it's a good idea to sign with one school knowing that you'll sign with someone else if a better deal comes along. If he has doubts about the NAIA - he shouldn't sign with them. In my mind, why would he want to if they don't have a degree path he wants. Some may disagree with me, but I feel like honesty is the best policy. The scenario you present just wouldn't teach your son a lesson you're wanting him to learn.
I will also tell you from previous experience (last year) that if he has college ability and schools are aware of him, your phone will probably start to ring alot in December/January. So, he shouldn't feel like he "has" to sign because there is an offer on the table.