Google has their own chips. Amazon do... Meta as well... Vertical integration is a competitive advantage worth pursuing for OpenAI. The spin is just that - spin.
This is instead a question of whether Sama preferentially made a contract with Rain, perhaps despite better alternatives. (Which would benefit him but might not be in the best interests of stake holders).
It’s possible it was the correct decision though, and his stake is just a fortunate side-effect, after all Sam is also invested in other chip companies (Cerebras I believe?).