With a companion i attacked a bandit camp in a snowy area and i started to approach stealth to test if yes or no companions go stealth
And it appeared that no, or at least the goblins saw us coming, because melee happened fast, and despite i was stealth i was spotted soon enough
I managed to kill 3 goblins with my bowman ally filled to death a few with arrows.
The goblin captain shot us, i was badly wounded (an arrow through the head) but my ally managed to shoot the goblin captain enough for him to run away , allowing me to escape.
After travel healing, here's my guy, i was wearing full armor but didn't found a helmet :
I went back to a castle nearby and finally found a iron helmet to replace my stupid cap. I hired 2 more companions there , decided to get back to the goblin camp and finish them.
Unfortunately on the way back we were ambushed by 5 night creatures, a family of "Man of Twilight" , they killed my 3 companions extremely fast despite my bowman ally managed to fill one with a couple of arrow and after resisting a bit thanks to my great armor items , despite my very good hammer skill i couldn't land a single hit, on the opposite they managed to knockout my guy (one was a wrestler that bite my arm off) and killed my character shortly after.
Looks like stealth is not anymore "none see me ever", good point.
Now will have to test more with higher ambusher skill (and no companion giving us away) to see how it still work with enemy reaction