Can AA create reports of Inactive Accounts filtering OUs ?
No, Active Administrator currently doesn't have the option to filter OU in reports of Inactive Users.
A workaround can be use here, where the undesired OUs can be excluded... but this will not only affect the reports, it will also affect the feature and exclude those OUs to process Inactive Accounts.
We have submitted an Enhancement request for this feature to be consider for implementation a future release of Active Administrator.
The Enhancement ID is 521956.