Does it make sense to use Acropolis in conjunction with a third party license key system?

No, Acropolis is specifically intended for hosting an Orion server, for Orion-protected applications. Any application that is integrated with a third party licensing system does not interact with an Orion server. However, if you leverage an Orion server for “tunneling” the distribution of legacy license keys through Orion licenses for operational efficiency, then it may make sense – this will, however, entail integration of your license delivery mechanism with Orion.