I don't see a big problem with creating empty artist tags. The artist name automatically appears on the upload page, which could be helpful when someone uploads art from that artist later on. It would be even better if someone creates an artist tag listing multiple websites from that artist, to save the trouble of looking for them later.
On the other hand, if the artist has even 1 post worth uploading, then maybe it would be best to upload it after all. If an artist has 0 posts worth uploading, then they probably don't need an artist tag.
Sometimes I've created a new artist tag and then uploaded a post seconds later, so I guess the new artist tag would seem "empty" for a few seconds. At least once, someone else deleted the new artist tag when that happened, so I had to undelete it.