No, Google Play Music (All Access or otherwise) is not the same thing as YouTube Music, though there have been reports and indications that YT Music may be planned to eventually replace GPM.
I still buy movies, and I have a fair bit of purchased music from before the subscription, so I'll be more than annoyed if I end up with my media library sitting in YouTube Red if they try to converge the products. Spotify would be high on a short list of alternatives if that happens.
Replacing GPM with YTMusic, unless the latter is updated to support everything, including personal music import and export, that the former does would be shady.
Giving me free YT Premium along with the GPM All Access I was already paying for at no additional cost is not, however, shady.
From what I understand, digital downloads from iTunes and the likes are basically just a perpetual license?
It won’t get you new stuff, but if you’re trying to fill your back catalog in, you can’t beat the price of goodwill.
nitpick, but it's “Google Play Music All Access”
I try to avoid getting sucked into Google's Ecosystem, but GAMA is pretty damn good. Sadly I don't know what the situation for GAMA looks like outside of the USA.
Edit:
But my point is, I hated Spotify, I still found myself forced to "acquire" music. This is the digital age, sell me digital music I fully own. People who don't want to pay for music will not pay for it no matter what you do. At least with Google when I buy music I can sync it to my local machine, but with GAMA I don't have to. The other upside is I get no ads on YouTube since I got grandfathered into YouTube Premium. Yes, I know, AdBlock, but I got grandfathered in to no ads, why would I care about AdBlock?