I seem to remember a similar discussion at my flying club about JetA and Diesel being used in compression ignition engines. The problem was sort of reversed because JetA is less viscose than diesel, but the answer we came up with is:
If in doubt phone the engine manufactures, and ask one of their engineers. If that draws a blank use JetA with no diesel.
It's better to pay a few more pence on the litre for fuel than to have a melt-down inflight!
WF.