The flickering problem has been well-discussed, it sounds like you have a good handle on what's up there. If I were you I'd consider flashing to the Asus 5870 bios ... it's the most brilliant thing ever, imho, presuming that your card is a normal reference version. Mine are also Diamonds, so I'd guess there's an excellent chance you'll get the same great results as I have.
Now, I don't know for sure it'll fix the flickering, but it'll make it so that your cards will run 'stock' at 850/1200 with a small voltage boost to 1.162V (iow, just like a 5870) without your having to use overdrive at all, so ... if using CCC OD creates the flickering issue ... I imagine you can see my line of reasoning here ...
As to the latter question, it's normal if you're looking at clocks in the CCC OD screen to see 0's for everything on the second GPU. It's a power-saving feature, new to the 10.2's. Basically the second card shuts off in 2d mode. Until GPU-Z and AB are programmed to properly account for this, you can expect to see strange readings for that card if you look in those apps. On mine, my second card shows as being in 3d clocks at all times. But I know that is not correct, rather, the CCC reading is actually correct. The card is shut down.
Which I think is awesome, personally.
And it has nothing to do w/the flickering, cause that issue's been around since day 1 w/these cards.