I'm still unconvinced that mankind CAN be Nemfected.
I think it would be really easy for a nemfected wizard to summon outsiders, as human wizards are the only ones who can.
Now if Cowl were nemfected, wouldn't it make more sense for him to go around nemfecting other wizards to summon more outsiders?
No, Cowl isn't nemfected.
He IS however working with Nemesis.