As you quite correctly state ES is not listed a a recommended optional rule for any scenario in any FWWC title, from my memory of testing these titles I think this was because of two reasons 1) With huge unit density in most scenarios adding in the additional layer of ES units would have made micro managing supply a real headache for most players and 2) the VST optional rules worked very well in representing the supply situation for both sides.
None of the FWWC scenarios were testing using ES, but that does not mean you should not use it if you can cope with the additional challenge that micro managing your supply brings.