Yes, I found this confusing and especially since the documentation seems to indicate that tags should be searchable. Given that it is not currently possible to add multiple creators to an item and that tagging seems like one nice possible workaround to this solution, it seems like it would be worth allowing tags to appear.
What follows is strictly my opinion/philosophy but I am very much of the mindset that redundancy is a good thing. I always want to err on the side of allowing more of the data that I have added to a system come back to me, who knows what I may search for years later that I happened to add as a tag, and why would I not want that to appear?