Yes, you would want to separate church from state here. It's best practice to separate them because SSAS is essentially another database that should be getting it's own set of resources versus fighting for them or most importantly, impacting other services. For example, management becomes easier. If the underlying system is impacted, it's not impacting both services at the same time such as patches, restarts, etc.

SSAS in the cloud is setup exactly that way now too I do believe. The only question is whether you break up your SSAS services by client, brand, project, etc.