It is possible to set up a single data sync to add and also delete records. However, to avoid confusion, we suggest creating one data sync to add collections and one to delete collections. You can do these at the same time without any issue.
If the data sync is a reclamation then you cannot have a two separate data syncs for add and delete at the same time. This is because the reclamation already deletes all holdings as part of the process.
More information, see Create an ongoing data sync collection.
The step by step workflow for data sync collections.