Nippert is a longshot to become a #2 or 3. I like Owings better than Nippert, though I think both will eventually (or could eventually) become the #4 and 5 in 'Zona.
Correct me if I'm wrong, but isn't Scherzer still unsigned? If and when they do sign him, I'd assume he'll become their #1 pitching prospect and could eventually become a solid #2-3 guy, but still, it would be a few years before he even cracks a Big League rotation.
Another good arm they have is Brett Anderson. I'm pretty sure he was a high schooler from the '06 class, but he has good command and pretty good stuff. Again, could become a nice #2-3 guy, though he is still a ways away and anything could happen.
Average depth in the pitching department, though most of them are still no where near contributing.