Thanks to the efforts of Emmanuel Dreyfus, the most recent version of
milter-greylist (v1.1.9) contains support for libspf-alt v0.3.  I
suspect that it will work ok for later versions, possibly with minor
tweaks.

Make sure you use 'configure --with-libspf_alt' to get libspf_alt
support. 


Please see http://hcpnet.free.fr/milter-greylist/