The way I understand this is that you can only purchase from a Cisco AND SimpliVity Partner where SimpliVity will handle support.
With the Dell/Nutanix relationship, it's reverse, you can buy directly from a Dell Partner and Dell will handle support. There isn't a requirement to be a Nutanix Partner, all enablement will come via Dell through Nutanix.
At least, this is how I understand it, a bit different in the support model.
I believe you can now buy the Simplivity licenses as a Cisco SKU so any Cisco reseller with the right partnership stuff can do it. I need to confirm that.
And honestly, I fully expect Cisco to just buy Simplivity at any minute.