I'm somewhat paranoid about corrupt save, not that I've had any trouble with them ever...not even on a royally-mucked up FCOM install! Lots of crashes and alt-tabbing causing issues (but never actually stopping me from progressing way beyond those points), but that's in the past. I'm now playing Nehrim, and yesterday I made a hard save (I never use quicksaves or autosaves, although autosaves are enabled) and immediately afterwards engaged an NPC in a conversation that leads to a scripted event. This wouldn't have done anything to the save, right? The 'save point' would be whenever I saved - not a moment later - and there's no danger of any corruption or anything?

It just saves your progress and the changes you made to the world. The fact that something happened after you made a save is irrelevant to the fact that you made the save.

If your concerned about save corruption, the first thing you need to is turn off the Autosave features. Even though you do not use them, I assume you mean you do not load them, they can corrupt over time and cause crashing whenever the game tries to make one.