I believe you should be able to upgrade from 7.2.0 to 7.5, but the release notes for 7.5 would indicate for sure. It may be best to go to 7.5.1 as that is now also available. 7.6 is available, but I'd personally wait for a maintenance release before considering moving to it.
As for your camera firmware, again, check the release notes for 7.5/7.5.1 and it will indicate the minimum firmware level they will need to be at. I would personally just upgrade the camera endpoints to the most recent firmware available to be safe.
Best of luck!
Scott Olsen
Solutions Specialist
Bulletproof Solutions Inc.
Web: www.bulletproofsi.com