Writing for Dungeon...
First question is, did you send a disclosure release form with the proposal? If you didn't, you'll never hear anything, because they will trash your submission. Legal stuff is the bottom line there.
Freelancing for any magazine can be frustrating, because the persons in charge of sifting through the gobs of material they get need time in order to give your submission real consideration. It'll probably take the crew at Dungeon up to twelve weeks to review your work and get back to you. (I think it says so in the guidelines, at least for Dragon.) If you have heard nothing in that much time, drop them a line ... that's not unprofessional after three months.
I'll give you some pointers on professional etiquette. It's completely acceptable to submit material
rejected by one publisher to another. It's unacceptable to submit the same material to two publishers at the same time, however. It's also unacceptable to submit material currently under review by one publisher to another or to submit an article on its way to publication to another publisher. (A contract usually handles things like this.)
On the flip side of that, it's been said, "As a writer, if you sell something once, you're still an amateur. If you sell it five times, then you're a professional." That doesn't mean selling the same dungeon hack five times, it means using the same ideas to write different things ... like a story, or a play, or a rules article based on a situation in the adventure you wrote.
FYI, I submitted two proposals to Dungeon in late May and I've yet to get the word, although the editor did let me know he'd reviewed my stuff and was about to get back to me before Gen Con.
Good luck with your submission!