For the sake of brevity I would say no way unless the MFG says it's ok and this general advice goes for all powders.

Hodgden does say it is OK to duplex a small amout of FFF with Pyrodex or T7 when shooting a flintlock or picky sidelock percussion gun. This is with loose powder and the shooter reducing the charge to make up for the added primer. For example you first put a little FFF Goex down the barrel before your main charge so you get better ignition.