I think it is great to take ANY opportunity to talk to an admissions officer whenever you can, and be impressive, respectful, enthusiastic.
Also, yes, it is great to tell the admissions officer that you posted on EssayForum, because it shows them that you are serious about collaborating and learning. I understand why you are concerned about plagiarism, because maybe the admissions officer will see the essay on the Internet and think you cheated, but like you said it's easy to just point out that it is your work with your name at the bottom.
You bring up a good point! People need to use their real names when they post here, so that they are shown as the authors of the work.
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Kevin, EssayForum.com