Just compiled svn16700 on Debian "lenny" x86, mod_fax loads and works perfectly. I have an ongoing compile on another machine (amd64) if It don't works i will send a mail (in 1 hour) otherwise consider it working.
How did you compile it? Using dpkg-buildpackage or via make/make install?
Do you have any debian versions of libtiff4(-dev) installed?