From what Mr Wild has said it would seem they are not associated in any way apart from RAW paying them to be featured in Battle of slots.
But i have also seen posts of Mr wild saying they will talk to RAW about their math models etc, which seems weird if its just some random provider.
I have never seen anything similar mentioned about other providers, which makes sense because why would a casino be involved in that in any way.
Officially its 'because raw has such good servers' but my guess would be that it probably goes a bit deeper than that, and purely by coincidence RAW slots are featured as 'popular' slots on VS website but i have never seen a RAW slot in the 'popular' category on any other casino, weird how that works.