Has anyone done actual inflight tests to determine the level of hazard? We used to regularly get our F-4 windscreens dampened with fuel while doing crossunders while the lead aircraft was dumping. Never a sneeze or cough from the J-79s that powered us.
I do remember an issue with the early A-4 Skyhawks swallowing too much fuel during certain malfunctions while inflight refueling from a drogue. (Putting a kink in the probe fixed that.)
I suspect that people are being a bit overly concerned about the dumping process. Swissair 111 would have had far better chances if they had put the nose down toward Halifax and just turned on the dumps.