It looks like you are correct. Exclusions take priority over scans. The listed article states that the asset will still be scanned to determine what it is, but the information is not saved in the database.
As I read it that means that a windows asset would be scanned, and if the exclusion is setup for workgroup or domain computers, that info wouldn't be saved. If an asset isn't a windows computer, that info would be saved in the database. I believe that the windows asset would have to be scanned no matter what to determine if it needed to be kept.
Now which takes precedence is the question. LSAgent scans or Agentless scans?
Only other way I could see to exclude windows assets is to have them in a separate IP range and not scan that range. Disabling the AD scanning options as well as noted earlier. Of course that depends on your environment.
What you're trying to do I believe is beyond the program's design. If any of the Lansweeper techs that haunt the forum have a better answer, please chime in.