I just tried the latest xemacs mailcrypt.  I chose encrypt from the
mailcrypt menu to send myself a test message.  When I try to read the
message in gnus (standard xemacs package), and choose decrypt off the
mailcrypt menu, it says: 
Found no encrypted message in this buffer.
Loading mc-pgp...done
Loading mc-pgp...
Loading mc-pgp5...done
Loading mc-pgp5...
I can see the encrypted message in this buffer.