I agree with Morno to a point, which is in a perfect world where pilots don't make mistakes and are perfectly competent the Multi Engine turbine should offer a noticeable level of safety benefit. However the stats prove that being multi engine in itself adds an extra element of danger in the real world where pilots do err and are not trained well and crash when the aircraft should have performed.
But then you go into things like pressurization. An unpressurized PA-31 is not going to suffer a depressurization event and loss of crew or hull, does that make it safer than the King Air, where several have been lost to pressurization issues just to achieve a more efficient, comfortable ride. That's where the comparisons between types get complicated and only rates of incidents over long term usage in like for like operation will tell the story. X has more engine failure accidents, but Y balances out because it has more handling accidents but Z is worse because of system failure accidents and so on....
Look at the ATR it has an appalling record of safety vs the Dash-8, SAAB and Jetstream, only the Braz comes close to it, because of the early propeller issues. I think even the Russian built turboprops have a lower loss rate than the ATR and those things are flown in horrendous conditions by questionable crews.