We need to define the terms though--when we say backup CF, do we mean a guy who can play in CF max 1x a week to give Buck a rest? If so, Kepler and Gordon are perfectly acceptable. If by backup we mean a guy that can handle the position daily if Buxton is out for 10 days on the IL, then Celestino is the only option anywhere close to big league ready.
That said, Upton doesn't change any of that, so if the Twins sign him, it is at the expense of PAs for Kiriloff, Kepler, Sanchez, and Sano. I don't think I'd rather have Upton getting PAs over any of those guys, all of whom have at least some upside that Upton does not, particularly when you consider that the Angels would rather pay Upton not to hit for them.