I suggest you keep posting to the forums so that our discussion can be shared with other readers.
is this following msg is true?
Note - Also please note that the Cascade Delete operation is applicable only for databases that support sub-queries. Cascade delete operation will not function for databases such as mysql and hsql, which does not support sub-queries.
The link is at: http://www.adventnet.com/products/webnms/help/developer_guide/topo/operations_on_mo/topo_cascadedeletion.html