Your starter will run backwards and the 2 cycle WILL run backwards. That isn't ok with the engine and the thing will have only one slow forward gear and 4 reverse gears but be rather quick backwards down the road.
That's an urban legend.
First off, the starter doesn't care about polarity as Sean pointed out.
The DD won't run backwards, not for long anyway. The blower will be running backwards as will the fuel pump & oil pump. Kinda hard for it to run with no air, fuel or oil.