Similar to South Dakota University, Mount Royal University (MRU) in Calgary, Alberta allowa public members to register in our leagues. Because Calgary has several local students, we find MRU students often 'round out' their teams with their friends from high school or other leagues. We do have some fully public member teams, but they're mostly students from other institutions.
With public members, they pay $90/sport as opposed to $40 that MRU students pay. We provide them with 'gate access' on their receipts (we use ActiveNet) so they can access the facility only during their scheduled intramural times. We understand that some individuals may take advantage of this system and use other areas of the facility but we've weighed the cost-benefit and decided we're okay with that. We also have member pricing for those who purchase memberships with us.
Allowing public members to participate is certainly a nice way to generate some additional revenue and provide various competition to leagues with lower registration numbers, but we have cancelled leagues which are dominated primarily by public members as we feel we're not serving the user group that we should.
Happy to chat more about any of this if you decide to make these decisions. Good luck!