Technically, FSF doesn't have a dog in the fight until Wordpress Foundation or whomever the license holder is decides to send a cease-and-desist to the developer of a style, add-on, etc. which is not in compliance with the GPL. Then FSF would offer up legal assistance and we're off to the races.
Again without going too off-topic, at one time, GPL was all about compiled binaries. I could not add my own proprietary code, recompile, and sell a GPL product as my own. Perfectly reasonable. Then the definition started being stretched.
Since PHP has aspects of execution which are similar to both interpreted and compiled languages, FSF have gone on record saying that include('blahblah.php'); requires both files to be GPL. They don't care if I'm making use of APIs. In fact, I've even heard that if you are aware of an API and using it, you must be GPL. Then more recently they completely went off the deep end and started indicating that adding a Cascading Style Sheet (CSS) would also be subject to GPL.
The GPL is a viral license and FSF seems to be taking the word "viral" and running with it. 