Each of the JEMS products are intended to be usable both as standalone products and as part of a larger architecture (SOA, ESB, etc). JBoss jBPM can be used by itself to do simple human task workflow, BPM, or web service orchestration, or it can be used with other JEMS products (JBoss Messaging, JBoss Transactions, JBoss Rules, and so on) as part of an SOA offering. JBoss jBPM can be used with other vendor's products as well.
I will call you about the specific questions about architecture approaches.
A request: As you answer various questions about architecture approaches, is it possible to mirror those back to this topic for the rest of us to enjoy?