They haven't said anything about the present vice admirals in the WG as far as I'm concerned. Aokiji and Kuzan (the hooded guy) were vice admirals at the time of the destruction of Ohara, but they moved up to Admiral.
If the new vice admirals are guys like Saulo, Aokiji and Kuzan, which they most likely are. Then I doubt that the weaker pirate crews that Luffy has faced stand a chance.
And Ohara wasn't just the tree. It's not like they just had to shoot the tree down and their done. They wiped Ohara off the map.
