The only real risk would be trying to pull too many amps through the PCI-E slot on the mobo. A short on the card could cause that to happen. IDK if motherboards have over current protection on the PCI-E slots. Also too much signal voltage from the card damage the PCI-E system on the motherboard.
Chances are, if the card is working currently on a different mobo, it should work on the new one without damaging it. Can you down clock the card to manually protect it and the motherboard?
I'm not sure how to go about down-clocking the card, but it sounds like it would be risky. I definitely consider damaging the PCI-E slot as a bad case scenario. Thanks for the answer, maybe I can borrow a GPU from somebody.