Well, you never stated it, but yes, there is a PC in the Indigo Plateau itself, at the Pokemon Center.
But otherwise, no, there is no PC whilst going through the Elite Four rooms, but you are able to switch Pokemon in your party, and thankfully, you can switch out Pokemon during a battle as well.
If you did mean a PC in Elite Four rooms, then sorry, but there isn't. That'd be nice though. :(