The ‘raw’ system is a discourse-specific thing, so you won’t find anything about it in the Ember guides.
It looks like it’s pretty deliberate in the core code, so I think it’s safe to use it:
In fact, it doesn’t look like raw outlets have the ability to pass anything like the ‘args’ you find in regular plugin-outlets. So context is the only way to go.
Please do feel free to make core PRs if you feel any useful data is missing in regular plugin outlets. Adding new arguments to outlets is relatively safe, backwards compatible, and has negligable performance impact, so it’s unlikely we’ll refuse.