We should be able to make an application talk to Resolve and Fusion interchangeably. Would be weird to have to have separate language for each product from the same company.
Especially since fuscript is so good and davinscript doesn't exist so it's not like there's a legacy base.
I'd be surprised if anything else was the case, as that would be a waste of developer resources and wouldn't offer anything to users except extra confusion.
Same thing with plugins, but baby steps, baby steps...