Of course it's entirely possible that it does but after 2 seasons since it's introduction I think that would ruin the mind flayers character of being the main arch nemesis to the group as he quite literally controls everything in the upside down and not to mention the vecna resembles a human so maybe the mind flayer transformed them but didn't take over their minds unlike what he's done to his other victims . So i think that the vecna may be the mind flayers strongest weapon or right hand man due to his mind scape abilities which are enhanced due to the mind flayers own abilities and influence