I would say that if a spirit goes to Skaukator, then anyone wishing to ressurrect that soul must go to Skaukator too, and speak with the Pale Lord or one of his subordinants. All spirits feel the urge to travel to Skaukator after a few days of being dead (with no gods, it often takes a while for the dead to get over the shock), and then it takes a while to actually get there. Until then, you can easily raise dead someone, unless their soul has been trapped, by spell or by fiend (need to figure out how to do this).
Actually, I'd say that we should wholly get rid of the time restraints for raising dead or ressurrecting, as long as the soul and body are both available. It'll just be a matter of providing rules for how far souls travel on their way to Skaukator, and how soon they leave after dying. Those who die particularly violent or dissatisfying deaths can become ghosts, uneasy spirits that linger despite the call of the Pale Lord.
After a soul has reached Skaukator, someone who wants to raise it must probably succeed in a Diplomacy check (DC 20, possibly less if the spirit is very well-known) in order to convince the bureaucracy to actually find the spirit. Then, the soul must agree to come back. This usually will require some familial or friendly relationship existing between the living and the dead. In some cases, the Pale Lord may simply veto a ressurrection, and he'll always know when one is about to take place. After a soul has been to Skaukator, the Pale Lord has full control over whether it can return from the dead. Spirits that have not yet reached the Necropolis can be raised normally.
Hmm. It's a complicated subject, and the one I'm personally most interested in. I was writing my whole story about it, until lack of interest made us cut it to reduce the size of Asgard.