The word "partner" lost its meaning completely. Each business relation is a "partner" these days. Guess it sounds nicer than "company that pays me to do stuff and bug you about"
I'm not sure all these relationships are monetary.
It may even be the case that the website pays X company to perform the tracking for their own analytics purposes. Or that it's X company's own freemium model where if you add their tracker they grant you a bunch of cross-site information for free.