As of iDisguise 5.7.1, you can disguise both players AND living entities.
To disguise a living entity, you need to know its Entity ID (EID).
When you type /odisguise and press the [TAB] key to retrieve completion suggestions, iDisguise will suggest the EIDs of all living entities nearby you (radius of five blocks).
Now that you know the correct EID, you can disguise the living entity using the command /odisguise …
E.g.: /odisguise  horse saddled custom-name=Hi,\sI’m\sa\shorse