Is Mac Finder PICTURES seen in Mac Photos?

Photos must be imported into the library before they can be viewed by Photos.

Here's some food for thought:

Bottom line: you can duplicate the Finder folder organization that you prefer in Photos itself.

Hi photos needs to import the pictures.

It can leave them on the file system as referenced files, rather than physically copying them into the library (in the same way as lightroom does), but there are so many problems with doing that, it cannot be recommended.

So if you're considering using photos, you should base that decision on the need to import the files into the photos library.

Yes. One copy in the folder where they are now, and one in the library.

But that is a good idea for backup purposes anyway. I never trust any library/database system with my originals. Storage is cheap. My photos are priceless.

Yes. But for safe purposes I'd move the source files from the Pictures folder to an external HD as a secondary backup, with Time Machine being the primary backup. That would free up considerable space on your boot drive.