"Can Horde queue up for Stockades and Deadmines, and can Alliance queue up for Ragefire Chasm and Wailing Caverns?"
Assuming you're in the appropriate level range, yes! There's no threat of a bunch of Horde zoning out of the Stockades in the middle of Stormwind because the tool drops you back where you queued, not outside of the instance. It's a good opportunity to see content that normally would have been incredibly difficult to access.
EXCITING! I have 3 dungeons left to run for the Classic Dungeonmaster achievement. Now what does appropriate level mean? I know I can't use the summoning stone for Scarlet Monastery. Does that mean I'll need to run to Gnomeregan? Does that mean I'll need to wait for 5 lvl-80's, or will it group me with some level appropriate toons?
Sadly, when I checked and I select specific dungeons, I see no dungeons outside Northrend. Guess I'll need to start walking..