It's all about branding and name recognition: they all profit from Redis via their cloud offerings. They have a strong incentive to support it and to have it as a viable open source project. Similar to other key opensource infrastructure.
Then their cloud-specific solutions are the up-sell (and lock-in).
I don't think so. The only thing they need to let their customers know is that they offer a memory cache service that is compatible with this or that interface. Whether it's Redis, memcache, Garnet, or whatever it might be, it matters nothing at all. All they need to do is ensure clients can consume their service, and that is it.
This whole thing sounds like a desperate cash grab that fails to argue any point on why it's in anyone's best interests to spend small fortunes on nothing at all.
Then their cloud-specific solutions are the up-sell (and lock-in).