Yes it does (in my experience with a caveat). A couple of my services deploy via github actions and I changed the registry over to the localhost:5555 one and it does seem to work. One thing to note about my environment is that I use a remote runner for the Github actions. I am not sure about using one of their hosted runners if that would work or no.

Regarding the different ports, you can do that, but it should only be necessary if you're concurrently doing deployments using the local registry. I haven't tried different ports since my deployments are inline.