I think Uva will turn out to be like Gooma from Kuuga. Why the hell would Arakawa keep a Zu Grongi around for 40 episodes?? Seriously...40 episodes Gooma was running around, getting beat up, only to temporarily take Daguba's powers, and get utterly destroyed in a column of lightning.
But I think Uva will have a bigger role. If anything, he will be the one who brings Mezool and Gamel back and in turn be the first Greed to be permanently eliminated.