IMHO the Asset Management 7 is just an add-on on top of a NS server. So Asset has to be installed on NS server. But workflow is a separated platform which can co-locate with a NS server or sit as a stand-alone which is recommended for performance.
You can install Asset on a second NS and make it behaving as a reporting server where the main NS server forwarding its data to this Asset server.
Really, it depends on the scale of your organization and the computing power of your servers.