Source on this? From everything I've read, only certain enemy types in SS1 will respawn in each level (e.g. only humanoid mutants on Level 1), and ONLY when their populations drop below a certain threshold, at which point a bunch of them will immediately spawn in. This is unlike in SS2, where there's an automatic respawn when each enemy type drops below a minimum threshold in addition to an ambient respawn chance below a maximum threshold. If SS1 had enemy respawns triggered whenever the player revived at a Cyborg Conversion Chamber, that would be much more interesting and balanced -- as it is, they function as less insane lemming rush/health regeneration stations a la Bioshock's awful Vita Chambers, as well as teleportation devices to get around the map faster. Granted, if you don't know the above fact about enemy respawns, the illusion of an ever-repopulating threat can keep you from wanting to use CCCs that way, and the fact that there's only one per map (and many of them don't revive you at full health) counts for something.
I'd love if anyone has anything more concrete on this -- I've just gone off what I've been able to find in forum posts and videos, as well as my own anecdotal experience. The now-released source code presumably holds the answer.