In a perfect world sure, but in reality what brings in those soldiers or unifies them could be and many times is more then a sense of honor, coin or conscription pay a big part as well. It's not coincidence that mercenaries, or "contractors" as they are known as in modern times, are all once soldiers unified under the flag of their home nation So unless a Titan can become a hunter I don't think soldier being Titan and mercenary being hunter is fitting