I don't really object to it, because it is within the rules and they are certainly open to all of us, but using 2013 players I think goes against the spirit of what "cup of coffee" player means. We won't know for several years whether these guys were truly "1-gamers" or whether they were just young players making their first appearance in 2013.
Again, no objection to using them within the theme rules as written, but perhaps for future seasons of the theme you might consider limiting it players whose 1 game happened prior to 2010 or something?