Lansweeper Ultimate and Lansweeper Corporate editions allow you to install multiple scanning servers which all can connect to the same database. In this case you only need a working SQL database connection between your scanning servers and your database server.
Alternatively consider if you can open the
required ports for scanning between your networks and use only one scanning server or if you can use
LsPush in order to scan Windows computers not connected to your network.
This KB article describes how to set up an installation with multiple scanning servers. You will be able to define scanning schedules for each scanning server individually.