If your already in the AF dep then legally an Army recruiter can't speak with you in regards to joining. You can however talk to your AF recruiter and drop out of the dep program. He may claim legalities about dropping out, sending you to jail, etc but ultimately he really can't doing anything about it. You are not under contract until the day you ship out to basic.
As far as joining the Army after dropping form AF dep, that's a tough one. The Army recruiter will know that you were in the AF dep whether you tell him or not. Everything is processed through the same system even though it is a different channel or route. Your name will pop up in the system. How they react to it, I honestly don't know. If I were an Army recruiter I prob wouldn't bother with you knowing that information. It shows the potential that after I go through all this effort to get you into an Army dep you may decide you want to be a Marine, Sailor, or go National Guard or Coast Guard. It's tough and I know it's a shitty way of looking at it but try to see it from their point of view.