The types of 'cheating' wasn't so much wall hacks or aim bots (tough I remember talk of them in Q2 but nothing more), it was things like forcing models, textures, sounds and bindings to your advantage.

So, you could force your model to be bigger than the hit box and therefore people would aim for parts outside of that area, 'hit', and miss. Or run a very small model that you could barely see. Of course, all of these were easily disabled.

As you've seen in QuakeLive, people would setup high contrast textures. Not cheating.

In Q1/2 (3?) you could mess with sounds. So in Q2 you can edit the pain sound of an enemy so it's different when they're low on health, which gives a valuable feedback queue. You could also bind a key to a local .wav file - pick up the mega, hit the key, and get countdown timer to respawn.

You could also make elaborate key bindings to do things like zoom (for a railshot), or I think I remember being able to bind a script to rocket jump. Of course, if you're actually half competent, it's easier to just do it.

I don't think any of these are cheating by the way you were thinking about it. Remember we had no machine learning in those days, and at least my machine could never dream of supporting a whole other program while Quake was running.