Theoreitically I think the app can use ffmpeg.exe in ImageMagick directory by editing the export batch command, "magick.exe" and "ffmpeg.exe" are mostly standalone executable, at least no dependency required in SpriteMacer. Currently I don't know how to make spritesheet/GIF/mpg natively without external DLL or EXE yet.
However, I think Steam users should not notice this tho, as the program runs as usual.