We removed an over the range microwave that was plugged into an outlet that was hidden in the cabinet above (installed by the previous homeowners). We are now going back to a standard range hood the requires hardwiring.
Do you see any issue removing the outlet and hardwiring the range hood to the wiring from the outlet?
If the wire is long enough just get rid of the box and plug your new range direct. If the wire is not long enough, remove the outlet and use it as a junction box, then from there plug your new range hood with the same gauge wire (probably #14/2 loomex). Since the junction box has to be accessible, you could put it inside the cabinets either above or beside the range hood (I usually install the box flush-mount at the bottom of the cabinet, and put a blank cover on it), or you could also hide it behind the new range hood. By dismantling the range hood unit you would be able to gain access the the junction box, and that complies with code regulations regarding accessibility to junction boxes. What you cannot do is put the box inside the wall, behind the gypsum board.