If you discount the Unowns on the top of the Citae (*cough*Level 80*cough), maybe. I know there are some high level pokes there, but some are low level (Like Bronzor).
Also, Unown does have some potential actually. You can create an Unown to deal with a specific type of pokemon. I.e, an Unown with HP Ice to deal with Dragons. Put a Choice Scarf on it, 252 Spec. Atk EVs and 252 Speed EVs, and you have a pokemon to murder Dragons.
The problem is that Unown stats are horrible, and anything with some kind of priority (Even Mach Punch on some cases) is going to destroy Unown.