Can you put RO services and DA services in multiple DLLs which are dependencies of the RO server exe.
How do you register these services?
For RO services you have to ensure that DLL containing service definitions are loaded into the application domain before the application startup. Just referencing an assembly doesn’t mean that .NET runtime will bother to load it at app startup.
For ApplicationServer boilerplate ( ApplicationServer Boilerplate (.NET) ) you can reference types of the service implementation classes as parameters of the ApplicationServer constructor.
For more advanced IHostBuilder based server infrastructure it will be up to you to pre-load these assemblies (either by loading them directly or by referencing their types from the code)
Additionally for DA services you will need to manually manage connections in case each service wants to use its own copy of .daConnections file