I have baked them in a crockpot before, but the result is not as crispy of a peel (the inside is extra fluffy and moist, though).
But if they are already baked, you can definitely keep them warm in a crockpot (well, for 30 potatoes in about 4 crockpots). If they're fully baked when you put them in, there is no time you must wait before eating; they should stay on "keep warm" indefinitely (up to 10 hours, easily), and if you only have a "low" setting they might start getting too done after about 3 or 4 hours.
If you are just trying to keep them warm a few hours - especially for that many potatoes - you can line a box with foil, put in the baked potatoes, cover with foil and cover with towels then wrap in a blanket to keep the heat in. That should keep them ready to serve for a good 2-3 hours, easily.
at 8:19 PM on May. 27, 2011