The text for Swaying word (8th level power of Conversion Inquisition) states:
Swaying Word (Sp): At 8th level, once per day you may speak a word of divinely inspired wisdom that causes a single creature to switch its alliance to you. The target must be within line of sight and able to hear you. If he fails his Will save, he is affected by dominate person, except the duration is only 1 minute.
So it can target any "single creature" but that target is affected by dominate person if it fails its save. Can you then really only target humanoids with the power or are other critters valid targets as well?