Excadrill was not Uber at the beginning of Gen V. Smogon unbanned a few Pokemon, all previously OU, in order to see how they would perform in OU with the new threats. Only the initial ban list Pokemon (Mewtwo etc.) remain Uber.
Also, you should note that Blaziken faces a threat from Gale Wings Talonflame, and Excadrill received a nerf as well; Sand Rush is no longer permanent. Smogon is basically seeing how these Pokemon will perform in a new OU, and if they're too OP'd, they get moved up to Ubers.
Smogon thread - Freed Ubers
Smogon thread - Gen5 Ubers in Gen6 OU