Naturally they will react to hits, if they can spot you - Mercs, for example, have superior vision to most of your units.
I'm at this point where pretty much everyone I go against: Humanists, Spartans, Guild security, Mercs, et all - all have units with superior vision, even at night. Just kind of immersion breaking since superior night vision is supposed to be the ubers' special ability. Like my camo'd units at night are getting shot by everyone from offscreen, on top of spinning on me when I do spot them and get them from behind, and it's just really tedious right now. Early game being sneaky/stealthy and creeping up to people to ambush them was really fun, but now it feels like the only reliable way to win missions is to camp behind my craft and lob out its inventory.
Enemies will turn around and shoot you if you hit them with a molotov or a black powder bomb as it damaged them. They won't turn around if you hit them with a primed frag grenade because it doesn't blow up til your turn ends, if they survive it they will try to shoot at you but you should have time to get your person into cover, or throw 2-3 frags to make absolutely sure they die
I do tend to use a lot of instant explosions, because priming something and throwing it consumes most of the TU percentage. Previously, I could use my forward scouts to lob molotovs, bombs, javelins/axes, then retreat back into cover - that's just not possible anymore.
I'll have to give the primed nades more use, but it just feels so gamey and demoralizing to explode people and have them spin and instagib camo'd girls at night. You'd think they panic, suffer consussions/shellshock, run off in fear, but it's like all the factions are now fielding hyperaware aimbot terminators with predator vision.
Now that the stealth tactics are out the window, it seems like I'd just be better off just armoring up as much as possible and fighting during the day. I mean, even the civvies/gangsters spot me the moment I start using fire arrows/molotovs at night, despite my units being well outside of the lit area (visually) ... why can everyone see so faaar at night?