But interpreting you more widely, if the aircraft component primarily associated with the momentum reduction is the reverser itself, why would anyone want to call the resultant force "inlet ...", or or "intake...." anything? Why wouldn't they call it "reverser vane load"?
Because that's not the case.
If blowing exhaust gasses on cascade vanes or reverser buckets were to produce a retarding force, we'd have a whole new law of physics at play (and we'd be revisiting Newton's third). We could transfer that new law to sailing ships, and let the ships use giant fans to blow on ship-mounted sails to propel the ship along.
Using a rearward engine-produced force to act on an engine-mounted or nacelle-mounted reverser mechanism to produce a greater retarding force is nonsensical.
You can certainly attempt to separate components of drag into lip drag, form drag, intake drag, or any number of other components of the ram drag equation (already provided, here); but it's largely irrelevant and meaningless. Particularly to one sitting in the cockpit.
Ram drag is a collective term which accounts for numerous components. One could blame the compressor, the diffuser, the intake, etc; "ram drag" is a useful collective term with a viable equation (again, already given here, with link provided) with accounts for the retarding value that is what slows us down during reverse action on the runway.
So far as exhaust mass gas flow being used to account for reverse thrust, it's the wrong flow. We're considering intake flow (hence, the acceptable use of "intake drag" or "ram drag," used here interchangably), not exhuast mass airflow. If we are to consider airflow through the exhuast on a high-bypass turbofan, we can only consider it as a portion of the mass airflow through the nacelle inlet; it's the mass airflow through the inlet that accounts for the retarding force in reverse operations. Considering the fuel flow in the equation, when it's only added to a small component of airflow through the engine assembly is important to the thermodynamic equation of thrust production, but not necessarily to reverse thrust. The chief value of burning fuel during reverse operations is to increase RPM and mass intake airflow, and thus intake or ram drag.