Yes you can, but a horror you normally would see, like those attracted by your horror mark, or send/summoned by blood mages, will disappear after battle, so enslave or not, you can't get it. There's only one horror you can normally see that will not disappear after battle- dream horror.
If I could actually keep them after battle, that would mean potential for horror factories on some of those artifacts, which would be a smidge overpowered I'd guess.
If I can enslave them as a way of potentially ending the battle, even without gaining a free horror, that would be perfectly fine for what I'm trying to do... (keep my wish spammer alive)