Snort-mysql on fc3 x86_64 is built without mysql support, resulting in failure to startup with error saying "database: 'mysql' support is not compiled into this build of snort". Also, the /usr/sbin/snort-plain and /usr/sbin/snort-mysql only differ by 32 bytes in size.
Found the problem and the fix. Turns out the make system is not picking up all the ./configure changes and therefore not re-building the plugins with the changes. The soluction was to add a "make clean" after each build in the spec file.
I can confirm that the same bug is present in FC5 snort-mysql from fedora-extras and that the suggested fix works for FC5.