To keep track of non-scannable assets you can use the "Save Pinged IP" option of the IP Range scanning target. This will create an asset page even if the asset can only be pinged.
Should an asset be set to a different state than "Active" it will be excluded from most built-in reports. However you can remove this restriction by modifying the built-in reports or creating a custom report. The restriction can be spotted by the following code:
tblAssetCustom.State = 1
Or
tblState.Statename = 'Active'
The built-in report "Assets: Asset to user relations" should give you an overview of all assets linked to an AD user.
You can also find the report here: https://www.lansweeper.com/forum/yaf_postst15153_Assets--Asset-to-user-relations--Built-in.aspx#post51403