Good question, and I cannot give you the exact NCAA rules, but I do know that coaches are allowed to hold individual 'skills' sessions with a few players at a time. I believe these sessions are permitted year around, but do not know if there is a specific limitation on the number of players that can be present for a session, the number of sessions a player can participate in, and the exact nature of the session. What is not permitted is to have most or all of the team present for a session or for the session to include anything like a 'scrimmage'.
The players can (and do) organize full team scrimmages during the off season and coaches are not allowed on the floor during these. I don't know if these can be observed by coaches, or if they could be taped for review (but I suspect not.)
Also - specific to this year, when a team has a summer trip scheduled like Uconn did this year, they are allowed a few days (10?) of practice prior to the trip - one of the big advantages to scheduling such a trip. Trips are only allowed every few years (once every 4 years?)