I can't guarantee this will be the case next year, but in the past and at other cons, singing (and especially if there's dancing as well) is involved enough to bump you out of the walk on category and into the skit category. And even if you don't qualify as a skit for whatever reason, you would still be eligible for costume awards as a walk-on.
I'm not sure what you mean by special program... if you saw that mentioned on the website, can you point me to where it was? My guess would be that special program refers to things like the halftime show or other specifically non-judged skits like executive staff performances. Those sorts of skits, by definition, wouldn't be eligible for any awards.