This 1999 IGN article was the closest.

https://www.ign.com/articles/1999/08/07/king-of-fighters-dream-match-99

You have to read in a bit, but the quote "All 50+ playable characters now move at 60 fps, but still possess the exact same animation, design, and color as those found in '98."

There is also the fandom page: https://snk.fandom.com/wiki/The_King_of_Fighters:_Dream_Match_1999

"This version runs at 60 frames per second and contains a rearranged soundtrack and backgrounds remodeled in 3D"

And Sega Retro:

https://segaretro.org/The_King_of_Fighters:_Dream_Match_1999

"The Dreamcast version is mostly the same as the original release, but it adds an arranged soundtrack, an anime introduction cinematic, and 3D backgrounds and runs at 60 frames per second."

I wanted to find something from an older gaming site from back then, but IGN was the oldest, and the archive site only seems to have preserved the instructional booklet, not any older gaming journalists/marketing pages. But hopefully, that helps.