The outer div from the advert has a data-dfp-pixel attribute with a value of a doubleclick URL. I'm not sure what that is about, but I guess it is for tracking.

The images themselves are coming from the imgix CDN for outline-brand so they do seem to be providing their own adverts, but maybe using doubleclick for some sort of engagement tracking. I'm not really sure.

Yes, but I didn't find that ad "out of place" or annoying. So I do not mind!

This site probably has its own ad system.

The way to go imo.