For Oceanic, they would have needed some sort of incentive to invest in the software development. An exclusivity agreement for some time would work. How long that is, is probably covered by an NDA.
When we worked w/Apple, there was no exclusivity. It’s just speculation, but I wouldn‘t assume that Oceanic has any kind of contractual exclusivity with Apple. For them to be the first/only Apple Watch dive app at launch, with extensive early dev support, co-marketing, etc – that’s already plenty of incentive. Don't forget that Oceanic already had a mature, existing codebase.
But beyond formal exclusivity, there’s also de facto exclusivity, which Oceanic currently has – and they knew up front that they'd have it for some period of time. Due to safety concerns, Apple will move slowly. I’d say that’s the real gating factor here.