This would make me a little nervous. Obviously this isn't much of an issue as long as the homes stay in the park (and he keeps reasonable tenants in them). It would be very expensive for him to move a substantial number of the homes out, but if he did you'd be scrambling to fill lots as I can't imagine this would cash flow well in that scenario. I would consider this deal if 1. the sale price and/or terms were smoking hot and 2. I was well capitalized and could fill lots with used homes (this is a lot of spaces for the new homes CASH program).
Better yet, is there a contract/lease you can have him sign to keep the homes in the park for X number of years?