I guess what could work is that the Guyver units were reverse engineered from Scarab armor. Zoanoids could have still been created to fight the Ohm, just not by the Daligigs. Sho is going to think it's the Daligigs until he gets some real answers though.

There's also the idea that Zoanoids and Guyvers were created so secret and long ago that few would even be aware of them. Regardless of who made them, they were meant to fight the Ohm.