Has anyone used third-party BHs with their Canopy system? Can they sync with Canopy?
Yes, No
GPS Sync, as implemented by Moto, is proprietary. As such, the only devices that can interpert, use, and forward the sync signal are devices that are specifically designed to do so.
Unless the hardware you are looking at specifically says “designed to use Motorola Canopy GPS timing sync pulse for TX/RX cycles,” its not going to.