Sting was the backup plan if Hogan didn't go for it, allegedly they did the "Eric got kidnapped" angle so he could stay backstage and make sure Hulk didn't get cold feet at the last minute.
At the time, the message board chatter was that while Hogan was wary about turning heel, he saw the writing on the wall that the Outsiders deal was going to become the hottest angle in the company and he wanted to hitch his wagon.