My sovereign captured a big spider with the studded collar in a tactical battle but by the time I had done that my hero and and sand golem had already died. However, when the fight ended by capturing the spider, my sand golem was back alive and my hero didn't pick up an injury. I am guessing when the battle ends with a capture the game doesn't register earlier deaths.
By the way, studded collar seems way too powerful. Does that work 100%? I found like 3 of them at the beginning of the game too.