I do not own Dawnguard, but it has come to my attention that there is lava present in a Dwemer ruin in this DLC.

My question is, is this lava animated? (does it move?)
If that's the case, is it a special mesh, or a water mesh?

Would it be possible to replicate this lava using vanilla resources? (with the addition of, of course, a lava texture)

It's animated, but what it actually is a mesh with no collision that is meant to go over a water mesh, which is set to look like lava. Then there's one of them box area things that is scripted to hurt and burn the player when they enter the lava.
So there's really 3 components. The lava mesh, the water mesh, and the box thing.

Additionally, it is possible to create the appearance of lava using vanilla resources and a custom texture, as discussed in http://www.gamesas.com/topic/1422577-non-dawnguard-lava.