Unless it changed with the latest code cycle that would be against code here, no returns in kitchens or bathroom's. It's possible that grill is hooked up to an exhaust fan but given the type of grill and placement i doubt it.
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Is it actually a return? I've put those grilles over ceilings that were damaged by overhead plumbing. Nobody but an HVAC tech would think it was out of place, and it makes future service easier. Hidden in plain sight.
