Someone ran some tests on another Forum with MGIV, there is a weak image formed just using an alkali. It's snot strictly developer incorporated.
What's being forgotten is that hydroqinone and its derivatives can be and are used as emulsion stabilisers, both Agfa, Kodak and Ilford use these stabilisers and there are books written on the subject as well as Patents and other research papers.
Hydroquinone (and derivatives) are used as anti-odidants in emulsions, they help prevent fog in B&W emulsions and are also used in some colour emulsions. Before WWII both Kodak and Ilford used Pyrogallol in commercial D&P developers alongside Metol & Hydroquinone, becase the Pyro was the stronger anti oxidant it acted as an oxygen scavenger and kept fog levels lower than if it was ommitted.
Eastman Chemical Company sells Hydroquinone (and derivatives) as an inhibitor/stabilioser/antioxidant in Photo grade as well as USP grade.
So Simon Galley is right that MGIV isn't developer incorporated that would require a much greater level, the addition of Hydroquinone or a derivative is ther for other reasons.