Problem 1. The voltages across most Analog Dimmer Potentiometers would probably exceed the maximum ratings of a Digital Pot.

Problem 2. Most Analog Pot Dimmers don't have the Pot isolated from the supply mains. So you will potentially be wiring your Digital circuitry to an unisolated supply.

It'd be a lot easier to take a PIC and design a Dimmer from scratch, than try to cobble two alien circuits together. If you are going to go down the route of your original idea, a good knowledge of your intended Analog Pot Dimmer is a MUST - many will not be suitable, and some could even put the Users safety at risk.