Looking at the article, it doesn't actually seem possible to get an "Extra" pick for Okung. What they are saying is that if the committee values Okung's contract at the entirety of the contract then we would swap the 5th round pick we are getting from Sweezy for a 3rd rounder from Okung instead.
Basically it brakes down like this:
We lost 4 UFA's in the offseason - Irvin, Sweezy, Mebane, and Okung
We signed 2 qualifying UFA's - J'Marcus Webb and Bradley Sowell
Those two UFA's we signed will eliminate the two lowest compensetory picks we would have recieved so...
If we would have gotten a 3 for Irvin, 5 for Sweezy, 6 for Mebane, and 6 for Okung (based on 1 year deal) Then the two 6th round picks would be wiped out by the signings of Webb and Sowell (Seahawks end up with a 3rd and 5th comp pick)
But if we would have gotten a 3 for Irvin, 3 for Okung (full contract), 5 for Sweezy, and 6 for Mebane Then the 5th and 6th round picks would be wiped out by the signings of Webb and Sowell. (Seahawks end up with two 3rd round comp picks)
Either way we are only getting 2 total compensatory picks because we lost 4 qualifying players and signed 2. The only way that changes is if somehow Sowell or Webb are found to not count towards compensatory picks. However, nothing I've seen suggests that either of them would not qualify. The Webb signing actually hurts us even more if Okung's entire contract is taken into account and we're awarded a 3rd for him because that would essentially mean we lost the 5th from Sweezy for the opportunity to sign Webb just to cut him too late to recoup the pick. We could have possibly had two extra 3rd's and a 5th...