Can Zombie Pigmen spawn on Soulsand?

I just realized that in all my time within the Nether I've never had a mob spawn in my netherwart farm. Now, while this would make sense after my farm was complete, because of the netherwart being on the block, it took my quite a bit of time to fill up all my blocks with netherwart. And in all that time (3-5 hours) I never got a single zombie pigman in my farm.

Can Zombie Pigmen spawn on soulsand?

Solution 1:

Mobs definitely do spawn on soul sand, the solid block requirement is for the block graphically, and soul sand graphically is a solid block (no transparency).

I did test it with a glass enclosed room with a soul sand floor and zombie pigmen did spawn inside.

Solution 2:

No

Nothing can, as it's not a solid block (it is only 7/8ths the height of a normal block).