Force Spotlight to index specific Library folders
Spotlight is already indexing those files and folders. You can check for the file names.

The actual problem is that the importer is ignoring the "code" portion of the files so the strings you want to find are not matching.

mdfind -name fmwebd_home.html


If you copy a html file to your desktop, you can play with editing them to include strings inside the body of the html - and see if spotlight can find things. Junk names like ZZtestZZ are easy to make up that don't return other spotlight matches.

mdfind  -interpret ZZtestZZ


Also, if you search in Spotlight graphically, you might want to save smart folders/searches that include the system files since they are normally suppressed from default searches.