Brook FP uses 'brokers' for underlying web functionality. This is the list, so it looks like Brook FP does use FCL's FCGI, among others.
% ls -1 brokers
brookfclcgibroker.pas
brookfcleventlogbroker.pas
brookfclfcgibroker.pas
brookfclhttpappbroker.pas
brookfclhttpclientbroker.pas
brookfclhttpdaemonbroker.pas
brookhttpdefsbroker.pas
brookmessages_ptbr.pas
brookstaticfilebroker.pas
Tardigrade/