If one game would qualify, that would be Alien Breed: the game switches from PAL to NTSC rapidly to emulate a damaged CRT display (extract of longplay at this point). A PAL to NTSC switch should occur at the top of a frame, so doing that in the middle of a frame can be considered like exploiting a bug.
Now, whereas games didn't push the tricks too far, that wasn't the case with demos, who always tried to push things with the various co-processors.
The co-processors are so complex that are a lot of cases where the behaviour is undocumented. WinUAE was often updated just to fix some borderline cases (sometimes not)
In some cases the author of WinUAE didn't want to imitate this.
COOL FRIDGE by UPFRONT
Running on Quickstart A500 OCS/ECS glitches on "SMOOTH COPPER" part an UPFRONT logo only when is copper plasma behind (see attach pict. 1 & 2).
We have a winner here! This has to be the most ugliest and weirdest way to synchronize CPU to display..
It WRITES to VPOSW to force CPU vs chipset sync! It writes to chipset registers in a loop, then increases vpos counter and writes it to VPOSW and then starts processing next line.
WTF? Why? This is too crazy..
I guess timing is close enough to real hsync and TV allows small jitter in hsyncs without causing display glitches.
I don't think I want to bother with this. It would require huge changes everywhere..
So, yes, demo makers didn't really care about using the machine properly or not. They tried stuff, and if it worked on a real OCS Amiga, then they'd use that.
Another example of a demo:
- Pax Americana by Complex -> (It writes to blitter registers while blitter is active ... impossible to fix without having blitter's original logic diagrams/schematics.)
If the programmers found a way to save cycles and cause bugs that either are not noticeable or even created a cool effect they used it.
Good luck to emulator programmers and new ECS/AGA machines to run those demos. Some demos can only run 100% perfectly on an OCS, unemulated Amiga.
So for demos, willingly or unwillingly, one could say that the bugs/undocumented stuff were exploited.