Well, it should according to http://www.via.com.tw/en/apollo/KT333.jsp
but apparently this isn't the whole story since in the chipset's white
paper only up to 266 MHz bus is mentioned.
Apparently official 333 MHz support was added with a later revision and
VIA conveniently choose to not mention it in the link above.

So, you're saying probably the KT333 will work with a Athlon 2800 @ FSB 333 but
it's not guaranteed by Gigabyte and VIA. Just increase the FSB in the BIOS
manually to 166MHz.

Mike