I also activated the mudmen after performing the dance of life, and Skanda still appeared. So I can't see that being a problem.

You do need to perform the dance of life in the correct room, though; I don't think performing it in the wrong room would 'break' anything, but it could be why Skanda hasn't appeared yet. Try doing the dance of life in the correct room (it's the very last room at the end of that loooong hallway), and see if that fixes it. (IIRC, you have to be standing in a certain spot too, I think in front of the tablet that tells you to perform the dance of life.)

Edit: I'm not 100% sure about this, but I think you might also need to do one more thing to summon Skanda. In G-3, at the center of the hidden area behind the mural, there's a warp point to the corresponding area in the Chamber of Extinction. Once there, there's a set of glowing jewels you need to activate (I forget how to do this). I seem to recall one of the tablets in G-3 saying something about activating Skanda, so maybe that's a necessary step too.