Yes capt dons there is no charge or rental requirement, same for Buddy's, and most of the other hotels. They just want you to drop gear, then go park, come back gear up and get in the water. They don't really want you hanging around the facilities getting gear on in case they are busy with their own guests. Divi I believe charges you for access and so might a few others. One place the charge include a towel and a drink. Kinda like a one drink minimum.Email Roger for the specifics. You can find his email under the diving section of the CD website. He runs the dive operations.
There was a sign that said something to the effect that outside divers are welcome but ask that you check in at the dive shop.
I suspect when the dive shop is closed you could simply walk in with your gear.
If you haven't been to CD or are not familiar with their shore diving set up just let me know. The main rule is there is a dive boat dock and a shore diving dock. Don't shore dive off the boat dock.
Enjoy your trip and post a report.