I am confused by the question of if you can ask future tenants to sign a lease during your DD. What you can do is:
1. Request estoppels of existing tenants in your offer contract. It is unlikely you will get a lot of participaton by current tenants but if some tenants give you the requested info it may help.
2. You can ask to speak with a few tenants during DD. This will answer all sorts of questions you may never get answered by the owner.
3. Walk through the park as much as possible. You will notice much more than you would driving through even 50 times.
4. You can request all the residents sign your lease after you take ownership
I hope this helps. - Kyle