re-read my posts above, you need an evap cooler instead of supply fan, we can talk circles all day, bottom line is if its on an evap cooler,on the hot days it will not be a problem. an air balance or "hood cert" will adjust supply vs exhaust.
As far as a return being to close to the hot air, we never put returns in a kitchen, and if we do it goes towards the perimeter or away from the equipment as much as possible, even by the managers office if possible, not sure if this is a walk up stand or restaurant.
there is nothing wrong with tha hanging plenums outside the hood or air curtain or whatever they have. you could put a scoop on it but if balanced right wont matter. the kitchen needs to have a switch that can turn the pump on and off in the cooler, when its cool outside, fan only works fine