Not true at all. Even if site owners embed ads directly as ordinary HTML images on the site that ad blockers can’t detect, people will ALWAYS have a way to opt out: Exiting out of the bloody tab!
And they will. People hate ads being shoved in their faces.
Remember, the SAFE Network rewards the site owner/developer in Safecoin as their site/app is used. The more users you can get on your site, the more $$ you earn.
Now consider this: Site A serves embedded, undetectable ads. Great for them.
Site B, their competitor, knows that people hate ads. So they serve none. Users will LEAVE Site A, and go to Site B. Site B becomes more popular than Site A.
Site B earns more developer rewards than Site A, because they have more users, because the users want content not ads.
A website will be more profitable on the SAFE Network without ads. It’s a free market phenomenon that will finally kill digital advertising (thank god), even if undetectable ads are still theoretically possible to implement. (And as @neo said, they will still be possible to implement in your SAFE grand advertising vision, so not even your own proposal solves your “problem”)