well, you can really be a sneaky bastard and act all surprised when they tell you that they are on the adcom. Just make sure that you can act. If you are one of those people that makes good impressions on people, then go for it. Don't over do it, don't try to kiss up while you are doing it either (if you were planning on doing this and kissing up, you are probably not one of those people that makes good impressions on people even though you think that you are, so I wouldn't do this), and don't do it for too long; just give them a taste and leave them wanting more, that's called good showmanship. Anyways, if you think you look better on paper like I always thought that I did, then no sense in endangering your chances by doing this and just shadow another prof. Actually, now that I think about it, shadowing another prof not on the adcom might be a better idea because if they get to know you, they can write a letter of rec for you. I don't think that an adcom can write a letter for you, and you never know if an adcom will speak up for you or even be there that day that they are looking at your app.