@OhWee - A minor correction, not that it really matters.
"Back when," there was a Daz Game Developer License. If you were going to embed meshes, etc., of Daz Originals in your Unity/Unreal/whatever, you needed to buy that - the rights to embed didn't come along with the asset itself. But that was a one-time purchase - if you had bought the game developer license, you could embed any Daz Original item. Some of the other PA's also offered similar "buy it once and you're good" Game Developer Licenses in parallel.
This has since been scrapped and replaced by the asset-by-asset "Interactive License." So now, to (legally) embed an item, you need the Interactive License for each individual item that you embed, as you correctly stated. One of Daz's comments was that "well, if you only want to embed one item, this is cheaper for developers." True, but for the vast majority of people I've heard comment, it ended up being more expensive. (Why is this not surprising? LOL) Fortunately, Daz grandfathered all the people who bought the older license.
But, as you also correctly stated, any
2D representation made from assets purchased on the Daz store are legal for any use. That includes animations that give the appearance of 3D motion, but are composed solely of 2D images. (There are one or two exceptions associated with
really old assets, but those assets clearly state that on their pages.)
As you also correctly stated, this concept doesn't automatically transfer to assets purchased on other stores - you have to review their license terms individually.