I'd prefer something more guaranteed. If, for instance, your hot engine hot hot engine is so hot it's begun diesleing -- you can shut off the ignition and it'l run on and so will the vacuum supply and ergo the vacuum-operated fuel pump. Ditto a mechanical pump.
If you're running nitromethane we want you to have a thumb/finger-operated shutoff on the handlebars, no variance allowed. If you're running nitrous oxide or race gas and have electric solenoids or fuel pumps -- the factory (or your own) electrical lkill switch on the handlebars is enough.
If you're running gravity feed, as long as you can reach the petcock shutoff with either hand -- while you're riding -- that'll pass tech.
If you're running nitromethane AND gravity-feed for the fuel -- you're a braver man than I, McGee!