I know from many blog posts that vCenter should not be placed on a dVS becasue if it is ever powered off it cannot be powered on due to not being able to allocate a port. What happens if your storage on a vDS but vCenter's networking is on a vSS? If HA is disabled and the host that vCenter is running on goes down will vCenter need to be powered up on another host before that host is powered back on. Basically a simple question, what happens to a host that uses vDS for storage if it is started up while vCenter is down? Is it able to connect to the iSCSI LUN's or will it need to wait for vCenter?
What I would say is that it would generally be far easier to maintain iSCSI on a standard vSwitch.
You shouldn't generally be sharing iSCSI with other network services, so VLAN tags shouldn't be required or regularly changing. This wouldn't be a situation you would gain from a vDS - so I would keep it simple and not do it.
But to answer your question, vCenter is required to change a vDS, it is not required to enable it. Your iSCSI should operate fine with the vCenter on a vDS. Except that you could make things very difficult if you accidentally broke that vDS and couldn't repair it without vCenter.
I see your point in keeping it simple with a vSS. In this case it would be a server with 2x10gb links and 2x1000mb links.
Would the optimal setup be vCenter and the storage for vCenter connected to a vSS and the rest of the VM's and storage for thoes VM's connected to a dVS?