In all seriousness, though, like Sildarflame said, it really depends on whether you mean PvE or EvE. I haven't done any exerimenting with hired units, but olags aren't really as overpowered as people think. On a flat plain, they dominate. Add a single tree, river, or ditch, and they are almost worthless (against players, at least).
Olags may benefit balance-wise from a decreased movement speed, but they aren't as overpowered as I think they ought to be. On the subject of extra hitboxes, I am not this level of programmer, so I have no idea, but a possible halfway point would be to have Ologs be almost completely resistant to arrows, but have a 5%ish chance that an arrow will do more than usual damage, representing a critical hit. This part may not be worth the effort, but you could also add a skill level for archer NPCs, that would determine their critical hit chance; i.e. a Blackroot Vale Bowman may have a 20% chance to critical-hit an Olog, but a snaga might only have 3%.