I’d rather say you can use skills to do RAG by supplying the right tools in the skill (“here’s how you query our database”).
Calling the skill system itself RAG is a bit of a stretch IMO, unless you end up with so many skills that their summaries can’t fit in the context and you have to search through them instead. ;)
RAG was originally about adding extra information to the context so that an LLM could answer questions that needed that extra context.
On that basis I guess you could call skills a form of RAG, but honestly at that point the entire field of "context engineering" can be classified as RAG too.
Maybe RAG as a term is obsolete now, since it really just describes how we use LLMs in 2025.