Yes that is correct.
We recently did some professional services with our prefered NetApp partner here in the UK and when we looked at the feasibility to moving to cDOT they said we would need temporary storage to move our current data whilst the NetApp is rebuilt.
We have a similar problem as our NetApp is our only primary storage device.
They did mention that NetApp/NetApp reseller do have the ability to acquire 'Swing kit' where NetApp will temporary hire storage out to a customer for them to achieve cDOT migration if they have no other storage available however this will come at an additonal cost but the costs are reasonable as NetApp are keen for customers to move to cDOT and want to make the transition as simple as possible.
My recommendation would be to speak to your NetApp partner or account manager.