That's correct. Enemies don't respawn.

UPDATE:
Yeah, I haven't been seeing any other enemies respawn, so it's plausible that either I made a mistake, or it was a glitch. I do often find myself doing experiments and reloading because this game doesn't tell us the expected results of things. So, I have to save it, do the experiment, and then reload to know if I want to do it or not. I may decide, "I like the description of this development," and then realize only after getting it that there's some caveat that makes it pointless for my needs.

For example, there are the enclosed areas surrounded by walls. So, my first thought was that I need to transport into them, but unbeknownst to me, you can't transport through walls. So, that would have been quite a waste of LP for my archery ranger character if I had not saved it first and tried the experiment. I do that kind of stuff a lot in this game. So, it's plausible I killed the spiders, and then forgot that I hadn't killed them before starting the experiment. I see enemies respawning in different locations. For example, the two forest spiders in the graveyard near the starting village have respawned since the last time I killed them. I think that black spider south of Aron's blacksmith home respawned once.