Why would monsters be interested in money? I hardly see Abizoah rocking up to the item store in search of some Kobold Pie, or browsing the antiques in Gregminster...The whole horse thing was mentioned in relation to how wealthy the enemy is so why wouldnt they be rich enough to employ "monster"? Also the "monsters" were referring to creatures you have to fight, including beasts such as yes flying squirrels and wolves (mukumuku and shiro). So can we just try and be a little less hostile when someone is giving there theories people?
I'd say Mukumuku and Shiro are explained cases, as they aren't being controlled, employed, or in any way forced to comply. Mukumuku follows Riou and Nanami, obviously knowing them from Kyaro Town. Shiro is a faithful companion of Kinnison, who he follows and fights with in the Dunan army. Whether or not he is onto it or not, he is fighting to protect the forests of Ryube (I think that was the reason kinnison gave, idk). Whichever other two 'monsters' you recruit, they follow Riou for their own reasons, although they would not have been able to do this without the listening crystals, whcih I think are for communication rather than controlling. The wolves in Muse were products of the Beast Rune, but I don't think they were controlled so much as 'let loose'.
So basically, the monsters on one side are 'explained'. If you have any ideas about how the enemy controls masses of monsters, do share.
(FYI: Bonaparte is adorable. That is all.)