Range Hood has plug, no outlet on the wall
It's common enough for range hoods to be supplied with a cord and plug.  It's also common for range hood connections to be made via BX. 

The range hood should be designed so the cord-and-plug connection can be removed, presumably exposing a standard 1/2" trade size knockout (more like 3/4"), and then the BX can be fit up to that with a BX fitting. There'll be a compartment that opens up to hook up the wires.