The same rules should govern grenade use by enemy or the player characters. I will say there are known issues with Grenade Launchers right now, but to my knowledge thrown grenades should be working. My guess is that the enemies probably won't throw unless they have a high percentage throw but we will check it out to make certain. We will also check on the damage on a missed grenade.
(FYI - I have definitely seen an enemy grenade miss)