No, Spatial was not doing that, they are an integration with Unity. Developers still needed to install Unity with a license, get the SpatialOS framework running as their net code, and then write a game.
Which leads me to believe they are installing or running the Unity Runtime on their servers? If not I'd love a better explanation :)
If I write a licensed Unity app and run it on SpatialOS, well, that's now no longer allowed.
Unity had a pretty clear model as providing a software stack that one pays for using, primarily containing a bunch of proprietary tools for creating applications for their runtime. And then one could package that runtime and their application and give it to whoever one wanted (as long as they followed the revenue share part of the contract).
So yes it's part of the stack. but it's the part of the stack that people are meant to redistribute with their game.