Based on what I have read, developers use Adobe tooling to create LiveCycle
applications, which run under a LiveCycle server, which is based on a J2E
application server such as WAS.
They're Java applications, which apparently have multiple ways of
communicating with a database server (JDBC, web service tooling, etc.). I
gather that executing merges and generating PDFs is done in the Java
application on the LiveCycle server - not the DB server - which may be
different from you might have imagined.