doppledoer - there are lots of moving parts here. When scheduling a playlist for each candidate song we calculate a 'user affinity' which is a value corresponding to how much we think the user will like the song. A bunch of data goes into this value including artist and song ratings, plays, skips, bans, favorites etc. We also calculate a 'user familiarity' for each candidate song. This is a value that corresponds to how familiarity the particular listener is with the item. This is based upon plays, skips, ratings, and so on. When we schedule songs for the playlist we take into account the user affinity and the user familiarity combined with the distribution, variety and adventurousness settings for the playlist to pick the best songs. So to answer your specific question, if the only piece of data we have from a user about a particular artist is a rating of '5', that artist will have a neutral 'user affinity' score, but it does get an increased 'user familiarity' score, since by rating that artist, we at least know that the user knows about the artist. Depending on the adventurousness setting, we may steer toward this artist (if adventurousness is low) or away from this artist (if adventurousness is high).
Hope this helps