The dragon helm does look very elvish.
I think if they have it in gold (or black) that would be great for an elvish faction.
Also, I like your idea for the dwarven helm.
It seems to fit nicely with that theme.
As for giving all factions of middle earth different helms,
I don't think that is strictly
There seems to be a bit of mixing with arms and armor in the stories and the movies.
Plus Rohan uses the ocular helms the most.