Can you teleport a monster vertically up and thus do them the D10 per 10' falling damage?
Yes, but they get a saving throw.
Teleporting them in the air counts as teleporting them into potentially damaging terrain, therefore they get a save. A successful save negates the teleport.
A type of terrain that hinders creatures, usually by damaging them. Examples: Pits, lava, and deep water. A creature can make a saving throw when it is pulled, pushed, slid, or teleported into hindering terrain. See also teleportation.
Yes. From the compendium:
*Irrelevant rules snipped*
If arriving in the destination space would cause the target to fall or if that space is hindering terrain, the target can immediately make a saving throw. On a save, the teleportation is negated. Otherwise, the target arrives in the destination space.
Afterwards, normal rules for falling would apply.