Hi June,
DataCare does not use program-specific integrity check settings, such as the IR setting that ignores completed POs. This is why the deleted items are appearing as integrity errors. To prevent these errors from occurring, you will have to add the items back into IC.
Here's an alternate suggestion for dealing with obsolete items. Until those items have gone through the system (such as completed Purchase or Sales orders) and been purged, you might want to simply edit the Item Description to something like 'DO NOT USE' or 'OBSOLETE'. This way, other applications or integrity checks that look for the existance of an item code will not complain when it can't find one.