While they were never exactly the same visually, they show up under the search field, have the same link and text structure...the only difference in the lightly shaded background

I'm not sure if it's my imagination, but the shading seems to have gotten a lot lighter. It used to be quite clear what was a search ad and what was a result, but now you have to look closely.

There's really no way to know that unless you work for Google. Some of the ads show up with a shaded background, maybe some of them don't?

That is basically the original meaning of "don't be evil", or at least the one used in the IPO documents.

You would probably know, since it's hard to sell ads like that without telling people.