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Although i don't know what the developers are/were using.

wd

For the XGA support I used the S3 documentation available here:
http://thorkildsen.no/faqsys/cates/video.html

From the pc demos faq( http://www.oldskool.org/demos/pc/pcdemos.faq ),
the ET4000 is considered a defacto standard: "(Many older demos use special hardware tricks that might only work on an ET4000; the ET4000 is considered the demo "standard".)"

As for games, the one I've been looking at is dawn patrol. It has support for two variants of et4k along with nine others vga chipsets but no s3. There's a fallback generic vesa driver but it wants exclusion of video address space from emm386(If there's a way to do this in dosbox I missed the blurb on how to do so; having searched vogons for an answer.)

Though I think getting the emm to handle inclusion/exclusion or some alternative should definitely be on a todo list, if not yet supported, since there's enough programs that make use of/require this like in dawn patrol's case, allowing the use of the generic vesa driver with the current s3 emulation, I'm still leaning towards ET4000 emulation for it's direct support.

I can tell you from experience that I found my Hercules Dynamite Power VLB (ET4000/W32p) to be a better card overall than my #9 Motion 771 VLB (S3 968). The ET4000 was as fast or faster (except in Win) and worked just as well, and was far cheaper.

On an unrelated note, one thing I've always been curious about is if any games adopted VBE/AF (VESA Accelerator Functions).

I think the Allegro library for DJGPP was able to take advantage of some VBE and VESA 3.0 features, so there may be some games made with that that use it. I think both of those standards came late in the game though, when Win9x was finally getting to the point of being able to run games decently.

"Dawn Patrol" works in Dosbox in SVGA.
You just need to have this line in your config.sys
device=c:\dos\emm386.exe frame=e000 i=a000-afff
(you have to boot from a hdd image of course)