According to the OU Sooners wiki site the 2006 team's (AP's final year) offensive philsophy was Multiple / Northwestern Spread.
So...you are both right. The used elements of the spread with AP there, but realized what a unique talent they had and used more "traditional" formations while he was there.
OU was predominantly a spread team before AP and they predominantly are after he left, but they did tailor their offense while he was there. Sumlin was named co-offensive coordinator prior to the 2006 season.
http://en.wikipedia.org/wiki/2006_Oklahoma_Sooners_football_team