I've got a good friend who left ther Teams for Navy flight school the same time I left for Army flight school. He's now flying Hornets for the USMC, and blends pretty well I hear cuz' he doesn't wear anything but his wings, Naval parachutist wings, and scuba insignia.
As for anyone other than Sailors attending BUD/s; it's the only school in Dod that is not open to joint attendance. You have to be in the Navy, and fullfilling a Naval Special Warfare billet upon graduation. The exception being foreign students who go through BUD/s (albeit with different grading criteria).
There are always several prior Marines each year who go through BUD/s, and have about the same successs/failure rate as any other demographic. Their skills as prior ground guys shine through when the classes hit the land warfare phase which is unfamiliar territory for most ship-borne Sailors. When I was instructing, I always made the ex-Marines boat crew leaders.
There are in fact about 6 ex-team guys in Army aviation right now, with another 3 or 4 guys in various ground roles. Three of us are at the 160th SOAR while the others are spread around the country. Technically, the Army prohibits wear of the Trident under some obscure uniform regulation I purposely failed to familiarize myself with. However, when I do wear it, it's only on dress uniforms, and goes above my wings. I have yet to be called on it. Talking to my fellow Team guys in the regular Army, they frequently wear their Tridents on all their uniforms to make the distinction that they have indeed been around awhile. If you didn't know, the Army is first and foremost badge whores. A soldier will briefly, but distinctly glance down the left side of your uniform before he decides how he'll address you. Welcome to the green machine!
Mike-