I'll defer to others with more experience with M. argenteus.. I only had them as juvies / sub adult and did not have any issues with them. But I've read on here others experienced an uptick in aggression / territorial behavior at maturity..
My experience with hets has been successful so far with older / bigger V. melanura and T. meeki in a 6 foot 240G. The hets growth started slow, but seems to have picked up some in the past couple months.. they're peaceful, active and love to bicker back and forth w/ the T. meeki.. but no interaction really w/ the melanura.. both the meeki and hets just kinda stay out of the melanuras' way except occasional non aggressive flaring from the meeki, cause that's how meeki roll..
One concern may be potential hybridizing.. I fortunately have not had that issue in this tank, but recently had to rehome an awesome young pair of V. briedohri "Rio Salado" in one of my 210G tanks cause the male kept trying to flirt w/ one of my older / bigger T. asfraci females.. when he started displaying breeding colors, and getting aggressive w/ all the other bigger fish in the tank, I rehomed the pair of breidohri... I doubt you'd have to worry about that w/ hets and meeki, but could be a concern w/ hets and any of the other vieja types..