In the early days of internet pirate sites there existed an argument that it was only the people distributing that could get sued for infringement. Similar when streaming happened it was argued that no copy was downloaded, and the users clearly did no distributing. With cable decoders (in countries without anti-drm) it was similar argued that no distribution occurred by the users or the producers of the cards.
Since then a lot of court cases has happened and as far as I know neither of those arguments have held up. There is usually a law or two that get digged up in order to have something to charge people with, and law makers has been quite diligent in address those kind of arguments in new laws.
But there is one major caviat. Those cases has all been by large media owners with both large teams of lawyers and "close" relationships with the legal and political system. A lone developer will have a much more difficult time.
It's rather that they're not distributing it (either source or binary) so the GPL doesn't apply to them. Not having access to the source doesn't exempt you from the GPL.
But they are getting an unlicensed product. IMNAL, but if they are made aware of the fact and continue to use the product, wouldn't it be willful misconduct?
What law would I be breaking in what jurisdiction? I’m not familiar with Somali copyright law, and that’s the main source of pirated, although I did read an increasing number in Nigeria too.
If you can’t go after them, going after their customers would kill their business.
But this approach seems too cute to be feasible even on the long shot that the GPL would allow it.