I know the stuff you mean - Maher's in Manchester have been supplying it all over the North-West of Eng-er-land for the last few years, and it sets like bloody rock once it's been wetted and Wacked.
However, it can be a bit claggy when first wetted, so we found it was best to use it as a fill material, and then dress the top surface with 40-60mm of DTp1, just to keep it clean until the laying course sand was put in place.
On a job in dead-posh Hale Barns some years back, we were instructed by the developer to use it without the DTp1 blinding, and we found it mixed with the laying course sand when we came to prepare the screed. This was probably because the job was done in high summer and the surface was as dry as a bone and very dusty, so the vibration of the plate compactor seemed to churn the dust and the sands together, somehow.
I've no evidence that this was detrimental to the pavement - we were never called back to deal with any ponding or settlement, but I did make a mental note that, if we used it again, we'd spray the surface with a hose before placing the laying course sand, to try and eliminate the mixing problem.
So, in summary, I'd say you'll be fine, but keep your eye on any dust problem, and make sure you get a nice tight finish to the sub-base layer before carrying on with the block laying.