WangFunk,
Lucky as pilots then, that we can't see what comes out of the back of the engines.
Jet fuel is pretty difficult to light with a match, I don't know how easily the vaporising fuel being jettisoned would ignite in flames/sparks coming from an engine. However, at the sort of speed required to remain airborne, I can't see fuel being dumped from a wing tip, getting close enough to an engine to ignite.
Further, none of the manufacturers would stay in business too long, if the fuel dump system caused the aircraft to catch fire or blow up.
An alternative dump, from a 747-200.