I would say that anything that pulls data onto your sites, without informing you is blackhat
I’d say the same for something the covertly puts up links for 3rd party sites.
It’s also quite possible that the disclosure is buried in the terms. But that’s the same way scumware got loaded onto computers “with people’s consent”.
Sure, setup a service that links back to great. Rotate a bunch of links, only if you tell the users directly. Run a bunch of hidden links for 3rd party sites, behind my back? :flush: