Zoro used Ryuo in Alabasta vs. Daz Bones already, it's a confirmed fact, because Zoro used the ability to "cut everything and nothing" as described by Koshiro, which later was described by Hyogoro as that Ryuo swordsmen use to cut everything. Obviously a strong affinity towards CoA. And in his 2 years with Mihawk, he had a lot of time honing his abilities and his Ryuo.
His power is the only reason he can use Enma. He is even said to surpass Oden. So why are bitches bitching here? :yasu: