Can Enderman Spawn on Slabs?

No, mobs cannot spawn on single slabs. This wiki article explains in detail the requirements for any given mob to spawn. To prevent endermen from making holes in your grinder, make the spawning level only 2 blocks high, or set mobGriefing to false.

Can Enderman Teleport on slabs?

I can confirm right now that they can teleport onto half slabs, btw. ... it shows that they only teleport 32 blocks. And that they can teleport to any blok as long as there is 3 spaces of air above it, except when there is water on it. (they also teleport to 1/2stone, air , air, air).

What can Endermen not spawn on?

Just like all other mobs, endermen need to spawn on a solid, opaque block. You can pave an area with half-slabs, stairs, or glass, among other things, to prevent them from spawning there.