Can you give a partner a chain blade to equip?

I'm not sure if there is still weapon limitations, but the partners are modeled after player characters. But the insane range and stun time of these weapons would let your partner pets to be unstoppable as a stunning machine.

they at the very least would only have the basic attack and thats it

You can't gift them to partners, doesn't show up in the list. :<

They're considered two-handed weapons, so nope.