Assuming that the pneumatics could be run off the propane, and that this wouldn't kill the efficiency of the marker (thus defeating its purpose) you now have the marker venting both hot post-combustion propane (and from the sounds of the user's manual, a couple sparks too) but also pre-combustion propane vapor. If the gun was still a pump, this wouldn't matter, but since this is part of a semi-conversion, at high rates of fire a flash ignition is something to consider. I don't think there would be a great danger involved, but one of the advertised safety features of the C3 is that flammable gas never makes it out of the gun, and this would certainly negate that "feature".
