this is in fact something i cant answer, for i display both my figures with the helmet on. i would suggest though that none of the regular neckless heads would sit high emough if, and thats a big if, the diameter itself would fit.
years ago i broke a coo model neck peg, which is internally attached to the body, i fear the damage here would be similar.
what i remember from various bodies, there were "rings" as accessories, never knew what they were for.
but i'd like to think if you got a head with neck you could slide a few of them rings over the
threezero peg and give it enough friction to keep it in place.
as for the brands i personally own, hot toys, coo model, kaustik plastic and aci, the neck often ends a bit below the ear/jaw line so there'd be a gap if the balljoint would pop in.
again, wild speculation on my part, i might be terribly wrong.
okay here´s a small edit :
these pics aint mine but they show quite well the visible head of the sculpt down to the collar of the vault suit
i think with any neckless sculpt there´d just be an unsightly gap in certain poses.
another example :
so far even their own sculpts from the game of thrones line seem to vary. for example i find a lose sculpt of the hound with a modeled neck, whereas eddard(?) stark comes without one.
same as this one, with the neck adapter having the opening straight at the bottom of the separate neck.
sorry i can´t give a definitive answer on this one