I imagine it would work pretty well. The thing is that the box size for an Alpha 12 is so large. A 4.5ft3 cabinet should be considered the absolute minimum size. Best to run Alpha 12's and 15's in huge boxes or open baffles.As for crossover, the DX25 is suitable for use down low, and the Alpha 12 develops plenty of output up high. I'd probably go with a first-order crossover, just like the one π, two π and two π towers.
Go with a 10uF cap in series with the tweeter and a 16 ohm 10 watt resistor across it. I'd probably size up the series coil for the Alpha 12 though, maybe use 1.0mH to 1.5mH to reduce the output above 800Hz. Just use a single coil in series with the woofer and don't use a Zobel. That way it isn't acting so much as a crossover as it is providing a reduced shelf above 800Hz.