John (or anyone else interested in the issue),
I’d be interested in hearing what you end up doing, or
answering any more specific questions you may have.
I am our main JSP programmer here and we currently also run
a pretty complex Drupal 6 site as well – the JSP site is www.christianvolunteering.org
and the drupal one is www.urbanministry.org.
Most of the communication we do between the 2 servers is just using a shared
database for the back-end, (using CCK types, taxonomies, etc), but we also do some
communication between the two sites in back-end Java code using the drupal
Services module (http://drupal.org/project/services)
with XML-RPC calls.
*************************
Ali McCracken