I have a Moto E Gen 1, will Republic Wireless add this phone to their line up of BYOD?
No, that isn’t going to happen.
Republic’s current crop of BYOP phones require Marshmallow (Android 6) or higher. Republic does continue to support Republic specific Moto Es as legacy phones. If the specific Moto E you reference is represented as working on another network or as unlocked it will not work with Republic. I doubt this will change as the Moto E is not on the list of Moto series phones to receive an update to Marshmallow. Details here: Republic Wireless 3.0 FAQs.