Circling back around on this, I decided to try the Hydra via 5-pin din and it works flawlessly. There’s something very weird going on with the USB MIDI on the Hydra.
Also, can confirm the RetroKits RK-006 is able to combine multiple midi outputs into a single stream that Hypno is happy with. Behind the 006 box I have OP-Z, Hydra, and NanoKontrol all working.