I'm using Spark with Reason 6.5 no problem, it even automatically picks the unit up.
Go into Reason prefs, go to control surfaces and click auto detect surfaces. It will actually pick up 2 sparks inputs, I think this is something to do with Public and Private ports. Don't delete anything, my Spark has 2 inputs in Reason.
Then open up your Reason midi implementation PDF and open the Arturia Midi Control Centre, create a new preset in you Midi Control Centre.
In one of the last pages on the Reason midi implementation PDF you can see the Midi CC numbers for the Kong pads. Map the numbers in your Midi Control Centre to represent the pads you want to control. This will actually then work for all of the drums in Reason as the Midi CC's are the same for all the drum instruments.
As mentioned on the thread, only 8 pads can be controlled, but how many fingers do you have?
I have set up 2 presets in my MCC. 1 for pads 1 - 8, and a 2nd for pads 9 - 16
Stu