Is following the topology:
Fax--FXS---VG224---mgcp----ccm4.0------mcgp----vg224----FXS---Fax
With above topology following would be the configs on VG224 for using Cisco Fax relay
MGCP:
voice service voip
fax protocol cisco
end
mgcp fax t38 inhibit
no ccm-manager fax protocol cisco
no ccm-manager config
Above is with no ccm-manager config. This would allow GW's to do Cisco Fax relay. I would recommend to disable ccm-manager like above config.
Also can they try Fax Passthrough to see if it works.
Following are the passthru configs for both GW's:
voice service voip
modem passthrough nse codec g711ulaw
end
mgcp modem passthrough voip mode nse
mgcp fax t38 inhibit
no ccm-manager fax protocol cisco
no ccm-manager config