That may depend on what your UKG automation is scripted to do. A few questions I would look at...Why did you delete the user instead of inactivate in Docebo? Why does the UKG automation think this is a valid user and therefore should be added? 

We don’t delete, we inactivate. If my UKG integration API runs and shows the user is active in UKG, but not active in my LMS, it will update the LMS and mark the user as active. I cannot inactivate a user that is still considered active in UKG. For us, that is appropriate.

agree with @lhubbard ...We have created additional fields to capture termination date and status as well + the script will deactivate the user when they are identified as terminated. Docebo does not charge for inactive accounts so it much easier to keep your inactive users in the system and maintain their history if you do historical repotting, comparisons, etc.

You can also think about moving your inactive users to a special branch if you don't want to see them or limit access for your PU’s, managers.

+1 for keeping as inactive, and moving to a dedicated branch, especially for at least time periods. Helps with a lot of things, could get into a longer term cleanup cycle if really wanted, something in line with your record retention policies, so like 3-5 years post deactivation actually delete the record.