I think I understand what you’re going for. Absolutely, if you don’t need to replicate these objects and can instead spawn them deterministically in identical places on the client and server workers then you would save a lot of network bandwidth by doing this. You were looking for a means to derive a new seed for each, but it sounds like you’ve found an elegant solution for that already.
With regards to the cost of many entities versus only gameobjects local to a worker; those SpatialOS entities will entail a large network overhead and additional processing whilst the gameobjects will require processing of their own on the worker. The resource cost of the gameobjects would be a static value whether they have matching entities or not, however, so avoiding unnecessary use of entities for them would be a win in terms of network optimization. The exact saving you’d get would be entirely dependent on their complexity and other implementation details.
I hope that helps answer your question.