Honestly, by the time you're ready to leave the academy, the people who helped you get in won't really care. All the active duty cadre will be at a different duty station. Your congressman sees a new bunch of applications every fall. He won't care if one of them tries to do a transfer 4 years later, even if he is still in office. Your elected reps have bigger fish to fry. I wouldn't go to one academy with the idea I was going to transfer to another service, but I wouldn't let loyalty to the admissions dept color my decision, either.
As far as the Marines are concerned, our percentage of TACAIR is pretty close to the Navy and Air Force. The percentages have been beaten to death, but the Navy is 50% r/w and growing, plus P-3s form a bigger slice of the pie than C-130s do of ours. The Air Force has very few helos, but it has a butt-ton of transports, tankers, BUFFs, and the like. Not to step on anyone's dreams, but if you are TACAIR or nothing, it's a tough road in any service. Even if you're good, it might not be your lucky week when you select. You'd better want to serve your country and fly. Getting your first pick is the bonus package.
Yes, every Marine is a rifleman, but I've been in for 9 years and have probably worn my cammies for a cumulative total of about a month, not including TBS and OCS. The flight time thing can be sliced a million ways, but I still contend that it breaks down more by type of platform than by service. My flight time compares favorably to AF helo pilots. Compared to transport bubbas, tough, I'm hurting.
Also, yes, we are part of the Department of the Navy. We're the MEN'S department. The USMC is a co-equal component under the SecNav. BTW, there has been talk of changing the name to the Dept of the Navy and Marine Corps!
Back to the original post. Have you applied for Marine Option NROTC? Remember, it's the end-state that's the important thing. If you want to be a Marine, work on making THAT happen, vice just going to an academy.