Half Dragon Orc...

[Tatterdash]

So, adding the Half-Dragon template to an orc bestows the orc with a Breath Weapon that does no damage? (It says the breath does 1d6 damage per racial hit dice of the dragon)

[David Fryer]

Generally speaking Humanoids don't get racial hit die. I would give them 1 racial hit die for becomeing a dragon and then they would get a 1d6 breath weapon.

[Lazaro]

A creature without racial hit die would add HD gained from class instead. So a 6th level Half-Dragon Orc would have a 6d6 usable 1/day.