Has anyone attempted to hash on CGminer on one card and cudaminer on another card, all in the same system? Is this possible? Or will I run into problems?
Totally possible, and surprisingly easy. Install the NVidia driver, then the ATI driver (installing the ATI driver first can cause CGMiner to not detect the ATI card properly). Specify devices appropriately in your configs, and you're good to go.
I run the displays on the NVidia card, so YMMV on that point. Also, note that PhysX will be disabled by the NVidia driver when you install the ATI driver - NVidia didn't take so kindly to people trying to run PhysX on an ATI card with some hacked up drivers a while ago, and their stance hasn't changed since. Afterburner/GPUTweak/Precision-X won't work properly with the ATI card (ranges from blank information on Afterburner to Precision-X program crashes), but you can get info from GPU-Z.
I'm happy too with current cudaminer interface (or lack off). The only thing I wanna see is an API level similar to cgminer, to have decent monitoring tools.
I think this is something cbuchner would end up having a personal motivation to do too, since he's on a 1.5MHash mining rig with 3x780Ti. Double extra bonus points for him if it's compatible with CGMiner's API for CGWatcher.