Being a domain admin is not actually required to scan Windows assets. What is important is being a Local admin. Aside from that there are some additional port requirements for identification and data retrieval.
Domain scanning requirements: https://www.lansweeper.com/knowledgebase/domain-scanning-requirements/
Additionally, you can do a test with testconnection.exe, which can be found in Program Files (x86)\Lansweeper\Actions on your Lansweeper server. Perform the test from your Lansweeper server to the client machine, submit the same credential used by Lansweeper to scan the client.