Does anyone know the purpose of the L-shaped bracket on the ground terminal of this Leviton 515PV plug? I could insert the ground wire to the side of the tab adjacent the green screw, but that might not be the correct procedure for connecting the ground wire to the terminal.

I think it is to ground the clamp and shell on plugs that have a metal cap. Look for a spring in the cord side of the plug that contacts that "bracket". On the "all plastic" ones it is probably cheaper to make one kind of plug assembly than the tab costs.