Precision Voltage Reference
As for supplying AD7545A with higher voltage, that should be alright. Don't forget level shifters for your digital inputs, though.

As for the reference voltage - you need an independent 12V voltage source to set the required output voltage range of the DAC. Not sure how to do this with AD584 - I don't see any obvious way. You could perhaps use two of them but they have to refer to ground (not Vdd).