It runs the Dimarzio in parallel/single/serie, there's quite some difference in sound.
I too have never used the tone pot, that's why i havent installed one, i was just afraid of all the things i hear/read in the net about using a 500K pot with a single coil.
The 250K/500K singlecoil/humbucker tone-dillemma is no big deal on a bass guitar. Although you might hear it, I think strat or tele bridge pickup might be potentially more spikey through a 500k than a bass pickup. A blend and the toggle will fit the bill.
Again, just flip the polarity on the SC when you hook it up, and stick with whatever gives you most output when using both PU's.
When using the HB in single coil mode, it should be able to balance nicely against your other SC - like a jazz bass.
Just make sure you take notes when you hook up!