While you can always assign either device profile or compliance policy using organization group (OG), technically you shouldn’t be able to do so for VPP app assignment.
Due to an internal bug per VMware support, however, this is possible if the OG already has some type of assignment mentioned above.
Per my conversation with VMware support, this is not encouraged at all due to changes in Apple APIs for VPP as stated within the assignment tab (underlined in red above). There’s already a request to remove this bug to avoid this confusion.
I happen to think this bug can be quite useful to streamline VPP app assignment without creating an additional smart group. However, one can never fight city hall.