Woden (and names) is certainly a psychopomp figure as is Karnonos. He and Woden both have a role in helping us use the riches of the Underworld and to get there in general.
I believe that Woden ect, spends more time going back and forth whereas Karnonos, who definitely CAN go back in forth, has a big job in taking care of souls/cthonic entities and keeping that realm safe- he may stay in that realm more often.
Karnonos takes the cthonic mystery and disorder and makes friends with it, allies with it. He doesn't destroy but placates and reasons with it. He helps us to be unafraid and to understand his realm and death and the afterlife.
Woden ect, can takes these things and deliver them to other realms quickly and safely, including us. But he doesn't just use the cthonic wealth and passages for us: he uses them to inspire warriors in his warband.
Where does Nantosuelta fit in? I think she's a generative force within the Underworld: she helps to pry it out of wherever, Karnonos watches and protects the whole realm and the things within, Woden can help it to get to us in a way that we can understand better.
Course the Underworld/Cthonic Otherworld is a BIG place and I don't believe that Karnonos has domain over it ALL, only the ordered places within the disorder. That he himself ordered and it was a big task. He still has to protect it from the shadowy places beyond.