Non-local suggests that you are issuing the command from a node that does not own the volume/qtree you are copying. Try to issue the command from the node that owns the volume/qtree, using a LIF/IP that is local to that node.
Re: NDMPCOPY from cDOT (source) to 7DOT (destination) problem
I've found the easiest way is to use the vserver management LIF of the node that the volume resides as your source hostname/IP. However, this is assuming you made one (not really standard recommendation until 8.2+). If you are using your cluster management LIF name or IP, then move it over to the node that hosts the source volume/aggr.
There are a bunch of other quirks you can run into, like whether the ndmp account you are using is a cluster or vserver level account. But since your authentication is successful, and it's just complaining about volume ownership, I would just worry about LIF location first.
For some reason, I have never been able to successfully use a cluster vserver/svm level account to authenticate to a data or intercluster LIF for ndmpcopies.