Ok. I mean, I know it works, but there are some conditions.
They won't throw over huge distances, so make sure you're within sensible throwing range when testing.
Also, they prioritise healing when line of sight is broken, so if their health is down and they have a syringe, they'll do that instead.
They also have a cooldown to prevent grenade spam so make sure the npc you're testing with has been alive for more than, say, 20 seconds or so.
Finally, make sure the grenade is a grenade - F1 or beancan, and ensure that it's in the npc's belt...not container main.
Might be worth redeeming the kit naked, just to be 100% sure.