Is it really likely that Vito would watched from the sideline as his rivals got rich from drugs? No.
Vito: "and good luck to you -- as best as your interests don't conflict with my interests. Thank you."
Exactly. I read that as a warning. Sollozzo probably did, too.
I think anything that increases the power of another Family would conflict with the Corleones' interests.
At minimum, Sollozzo had to consider the possibility that Vito would use his political might against him. That's why I think the hit would likely have proceeded regardless of Sonny's outburst.
