I've got a running 3.0.25a PDC over OpenLDAP, but winbindd -d4 will claim "could not open handle to NETLOGON PIPE" when queried with wbinfo -t. I examined the problem and found:
cli_rpc_pipe_open is called with cli=0, because init_dc_connection doesn't initialize it on the local machine.

My hack is patching winbindd_cm.c:cm_connect_netlogon() to temporarily force domain->internal to zero before calling init_dc_connection(), but I guess it really should call init_dc_connection_network(), with the check for internal domains moved from init_dc_connection_network() to init_dc_connection().