An aside on grad program funding
osdad, post-grad opportunities, programs and costs for officers from any commissioning source can be a complicated thread on its own, whether just after commissioning or during the career. Lots of variations.
For purposes of this thread, and from my Navy knowlege, yes, there are some IGEP (Immediate Graduate Education Programs) that require the applying 1/C midshipman out of USNA to produce 50% of the funds (grants, scholarships) for certain programs, such as Cambridge, Oxford, Trinity. This is based on what I know of some '09 and '10 sponsor daughters who were approved to apply for these programs; they had a lot of legwork to do to raise the matching funds. Others, such as Naval Postgraduate School and USUHS (military med school), are fully paid for by government funds. There are Tuition Aid programs for those officers and enlisted personnel who have a full-time "day job" on active duty. They take college courses and post-grad courses at night or on the weekends in Navy-approved majors or degree areas, and submit costs for partial reimbursement by Tuition Aid. There are other full-time grad programs, such as CNO Intern, Naval War College (which also has online and homeport seminar programs for those not able to go full-time), Naval Academy Company Officer Master's program, other professional and staff colleges, and a few more cats and dogs. I won't even address the JAG or other staff officer opportunities, or the VGEP program at USNA.
The majority of line officers gain their post-grad degrees during their first shore tour after initial sea duty. It really doesn't matter when, but it's prudent to have one in hand before the O-5 promotion board pops up. Many officers have career paths such that it's difficult for them to spend 2 years ashore as a full-time post-grad student. If they are hot-runners, the Navy ensures they have an opportunity. We had a sponsor daughter, Surface Warfare, who came ashore for her first shore tour as an instructor at a school in her own community - very good duty. She started working on the Naval War College online post-grad courses, but was plucked out of the tour after 1 year and sent to Iraq on a one-year IA (individual augmentation) tour on a joint staff. Earned rave reviews there for her work, adding to her already stellar record, and the Navy excused her from her 3rd year as an instructor and sent her to grad school full-time on a one-year program at a prestigious civilian school, Navy's nickel. She's now headed for the XO/CO pipeline.
Most of the time, yes, they also receive O-1 pay and allowances. I do know of a few programs, such as the Law Education Program (LEP), where some of the approved applicants from the Fleet and Corps get the full school ride and retain pay and allowances on active duty status, and some get the ride but are placed on inactive reserve and receive a small stipend, but not full pay and allowances. Ditto for some med school programs for officers applying to laterally transfer, in terms of USUHS being a full ride with pay and allowances, but the civilian schools are full ride but IRR status - I defer to KP2001 on that, as much changes with the needs of the Navy. If the Navy needs more of something, more dollars get authorized.
So, bringing it back to Golden Key, for those few mids who are approved for IGEP out of USNA and who choose to go that route, it could be a source for matching grant money, though I don't have specific knowledge of that.