I've checked plugin and only what comes to my mind is this index created on oc_t_item_bo_mgr table:
FOREIGN KEY (item_id) REFERENCES /*TABLE_PREFIX*/t_item (pk_i_id) ON DELETE CASCADE ON UPDATE CASCADE
Once plugin is uninstalled, this table is dropped, but as far as I know it does not work in 2 directional way.
I've done test and removal record in oc_t_item table trigger removal in oc_t_item_bo_mgr.
But removal in oc_t_item_bo_mgr does not trigger removal in oc_t_item table.
Plugin, however, can cleanup disabled, spam, inactive and expired listings / users (depends on your settings).