I see two cases in the logs where Sonarr asked SABnzbd to remove a release with that name and in both cases SABnzbd responded indicating that the release was removed:
15-10-29 13:32:18.3|Debug|SabnzbdProxy|Url: http://localhost:8080/api?mode=history&name=delete&del_files=1&value=SABnzbd_nzo_ze979d&apikey=<removed>&output=json
15-10-29 13:32:18.4|Trace|SabnzbdProxy|Response: {"status":true}
15-10-29 20:21:13.7|Debug|SabnzbdProxy|Url: http://localhost:8080/api?mode=history&name=delete&del_files=1&value=SABnzbd_nzo_z-_rka&apikey=<removed>&output=json
15-10-29 20:21:13.8|Trace|SabnzbdProxy|Response: {"status":true}