The connector in question is for a backplane power cable. The necessary watts are probably there, however, I can't find if this is an EPS connector, or an 8 pin PCI connector. They're keyed differently, so they would not connect with one another (bottom right pins are shaped differently). Considering the location, I would expect it is a 8 pin PCI connector, but I would still recommend proceeding with caution because the 2 ports look so similar, even if they're meant for different things. The important callout being that some of the voltage rails are reversed, so if an inappropriate cable were plugged into the connector, it could short circuit. I can't find any definitive information about that connector, since it's meant for a different purpose. Pinout details for the connector aren't available. I'd look at one physically, but don't have one available right now.
Speaking generally, most servers we have that support GPUs include a GPU enablement kit. Part if that kit are the connectors to power a GPU. Despite what we see in that guide you linked to, I don't see that we ever sold any GPUs for the server, nor a GPU enablement kit, an dour slot priority matrix doesn't list a GPU classification, either. If you decide to continue, just be careful to confirm that connector is PCI.