The people providing the exit points for Oxylabs and Luminati do not know they are acting as exit points, nor would they actually approve of it if they knew what it meant.
Oxylabs have a public stance about doing it in above-the-board ways (https://oxylabs.io/blog/standards-for-proxy-acquisition) but I guess you're saying this is BS.
For the actual end user it's definitely not above the board.
Public notes:
https://www.reddit.com/r/androiddev/comments/ao27tu/my_app_w...
https://www.reddit.com/r/androiddev/comments/ajfc7w/question...
https://dx.doi.org/10.14722/ndss.2021.24008
I have never seen actual informed consent before in ANY of these for the final end user; most of the targeted apps are general rubbish (think flashlight app requesting location permission and contacts type of BS). At best it would be buried deep in a ToS or EULA somewhere, and even that's fairly rare. Using a very very stretched definition of rewarding users, you could argue that "allowing the use of a calculator for free" is the reward for being an open proxy.
If you find any example anywhere by the implementors ("oh, it's the sdk includer's fault they aren't saying anything, we're totally above board...") that there is anything approaching informed consent, I would love to know some examples, because I've never seen one in these. (I would dearly love to be wrong here)
There's still a remote possibility that they have changed their behaviour, since their post about end-user awareness and monetary compensation is somewhat newer than your references, but at this point I would need some independent third party vetting about that to convince me.
But it would be interesting to know what these companies do to cut down abuse and results thereof...