Uldred didn't rebel, he was possessed, if you forgot that tiny detail, So "Uldred" was more concerned with random acts of violence instead of actually rebelling.
Having just beat that section, all Uldred was doing was trying to get the Circle to align with Loghain after Ostagar, and the Circle as a whole nearly did, when Wynne came in and told Irving the truth, so they called Uldred in and confronted him, and he ordered an attack of blood mages when things weren't going his way, summoned a bunch of demons, and got possessed, and started making more abominations.
It was a rebellion, but it didn't start out as one, and wouldn't have happened if Wynne hadn't survived Ostagar and came in and told Irving (who nearly went along with Uldred) that Loghain retreated at Ostagar and abandoned the king and the wardens to the darkspawn.