Yes it is specifically the part of their stack that one distributes to customers. It's like if the Java runtime or the DirectX runtime wasn't distributable to cloud machines.

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.

The EULA bans any SDK, not specifically the GDK which presumably includes some part of Unity in a re-distributable form. If it was only banning the GDK, then developers who want to use SpatialOS could integrate the SDK on their own just like someone who uses CryEngine or builds their own engine instead of using either Unity or Unreal for which the GDKs were created to streamline the process. But the EULA doesn't stop at using Unity on the cloud with an SDK, it bans all use of Unity running on the cloud. "2.4 Streaming and Cloud Gaming Restrictions. You may not directly or indirectly distribute the Unity Software, including the runtime portion of the Unity Software (the “Unity Runtime”), or your Project Content (if it incorporates the Unity Runtime) by means of streaming or broadcasting so that any portion of the Unity Software is primarily executed on or simulated by the cloud or a remote server and transmitted over the Internet or other network to end user devices without a separate license or authorization from Unity. Without limiting the foregoing, you may not use a managed service running on cloud infrastructure (a “Managed Service”) or a specific integration of a binary add-on (for example, a plugin or SDK) or source code to be integrated in the Unity Software or Your Project Content incorporating the Unity Runtime (an “SDK Integration”) to install or execute the Unity Runtime on the cloud or a remote server, unless such use of the Managed Service or SDK Integration has been specifically authorized by Unity. Additionally, you may not integrate the Unity Runtime with a Managed Service or SDK Integration and offer that integration to third parties for the purpose of installing or using the Unity Runtime on the cloud or a remote server. For a list of Unity authorized streaming platforms, Managed Services and SDK Integrations, click here.This restriction does not prevent end users from remotely accessing your Project Content from an end user device that is running on another end user device. You may not use a third party to directly or indirectly distribute or make available, stream, broadcast (through simulation or otherwise) any portion of the Unity Software unless that third party is authorized by Unity to provide such services."

So what?