Anyways it's not dangerous to use one 8pin connector but I gotta tell you that it's not going to work, the gpu won't display any shit, 2x 8pin was planned for the gpu for a reason, it's like you saying the manufacturers don't know what they are doing
None of the more recent cards work with one less 8-pin plugged in, but I think almost all of of my RX580 cards that had 2x 8-pin or 8-pin + 6-pin worked fine with only one 8-pin plugged in. I can't remember all of them, it wasn't many. One was a Sapphire.