PopTime - That is correct - they are free to call, etc. Like ahsbb said, I think that perhaps some DI coaches resent this. It was a retired DI coach that recommended my son to a JUCO and when I told that coach how Michael loved spending five hours on the field with the coach and the team, he just laughed and shook his head "Oh those JUCOs can do that". I remembering thinking that this was an unfair advantage for JUCOs and NAIA that the rules were not the same. However, in hindsight, I realize how many parents/players have their minds set on a NCAA route, that perhaps the other schools do need this difference to be able to compete in recruiting.
While this isn't scientific, I'll share my thoughts on NAIA recruiting timeline with you. My HS '05 son was only called by one NAIA last fall, which we did visit. The only other schools that called at that time were DI/DII. However, after the early signing period, he received letters from 4-5 other NAIA, and calls from 3-4 more with one of those going to the top of his list. So, from personal experience, it would appear that perhaps NAIA schools delay recruiting a little longer than NCAA schools (at least DI). I'm making the assumption that some may wait to see what kids have early offers/decisions and go from there. I don't think that NAIA, unlike some NCAA schools (again, particularly DI), recruit a year or so in advance due to money. They don't have the budget to follow kids long term for the most part. I had a DII coach tell me this week that while SEC schools for example, may follow a kid for a year or two before they recruit him, that his school didn't have the manpower or funds to do that. I think this is true for most NAIAs. They begin closer to the actual time they need that recruit.
Part of my son's recruiting journey that I think we didn't do correctly was to have a school/schools that HE wanted. He chose from the ones that came after him. It worked out for him, but I'm not sure that's the case for many. So, if there's a school that your son is very interested in, especially NAIA, since they have fewer restrictions, I'd tell him to go after them full swing. Get that letter in the mail, call and follow up to see that coach received it. Make a visit and ask if you can work out. Invite him to any showcases/camps this winter. That coach can come wherever he wants this winter without restrictions. I do think coaches want kids that want to be there - I think NAIA coaches are especially sensitive to this. Best of luck.