I don't see any scenario where that would not be supported. If you think about it, you can have your ESXi hosts that are contributing vSAN storage just be storage and have other hosts in the cluster not contribute storage. Your biggest problem is bandwidth to all of your storage. But anyway, it is absolutely okay to have VVOLS storage from like a 3PAR and also have VSAN storage from some hosts with SSD drives.
Here is a similar communities thread. Re: Can VSAN hosts access FC-SAN storage in the same time?
Is there are particular deployment you are considering?
