Phil, I asked Jonas about this, he maintains fpc for MacOSX and that script.
He told me (in Dutch, so this is a translation) that XCode (= developers tools, has *nothing* to with the X11 SDK) installation package is a "meta package", which groups several other packages. As long as you don't deselect certain packages (e.g. gcc 4.0) manually in the installer, everything works ok (all this goes for 10.4 and earlier versions).
Although FPC doesn't need gcc is a strict sense, if you use Xcode with fpc you do need it (because FPC compiles only to assembler under Xcode en Xcode calls the gcc driver to assembler those files). So in the long run, disabling the check for gcc will give more problems than that it will solve.