Yes, you can QSM non-tree data also. When specifying non-qtree data (ie: all data that's in a volume that isn't in a qtree), use the below in your snapmirror syntax. Also, pre-create a qtree on the destination for all this data to go into.
/vol/-
The hyphen captures all non-qtree data.
This way, it's just a straight snapmirror, don't have to do rolling changes.