Ok so when it comes to partners cards, having a hole in the back plate should not negatively impact thermals as if that hole is blocked due to the psu, the card will just exhaust normally like normal cards, HOWEVER this is not the same for the reference, for the reference card the fin stack looks to be completely surrounded (by metal or plastic) this is so the only way air CAN go is through the hole in the backplate, if that hole is blocked then that heat cannot escape.
i wouldn't worry about partner cards having a hole in the back plate as they should perform decently regardless, however if a card is designed ENTIRELY on all the air escaping through that hole like the reference, then id be cautious