Doing a different 3d model for all henchmen types for every single race might be the reason they went this way for henchman, however a possible solution could be to have Altar-style Henchmen for all races - "these special units seek out every heroic race with sufficient influence" or somesuch. With Juggernauts, even though they look like extra-ugly Trogs, I don't see why it would require a Trog blood type pre-requisite, as theoretically any race could breed monsters - but maybe trained Juggernauts (as well as the monsters Escaped Juggernauts) could be "Twisted" race too, rather than the race that trained them. This would give any champion type unit with "+ Attack versus Twisted" Weapons an easier way to take them down. And they ARE tough to take down, it might be good if there was a little help. 
So yes, I think that there shouldn't be both a blood type AND a trait prequisite for any special unit, and there certainly doesn't seem to be a technical reason that can't be worked around with lore, etc.
