If you are talking about scanning all devices in a DMZ (aka not just Windows devices), you would need to set up an additional Lansweeper scan server within the DMZ, and then make the appropriate firewall adjustments to allow that server to communicate to the SQL server which hosts your Lansweeper database.
If you are only interested in Windows devices, there is an agent that can be installed which essentially gathers information, uploads it to a cloud based repository, and then your local Lansweeper instance synchronizes that data.