Hi Simon,
An entirely accurate description is going to take more time than I have at the moment. The tools the project was using needed additional functionality and/or patching to make things work in ways that others support already. Fortunately, the configuration is conventional and similar to other infrastructure commonly used for Java development. I drew up a diagram for a migration proposal for my prior employer, and the pieces are configured very similarly. In the diagram, Nexus == Archiva, Jenkins == Continuum.
As for the account management, we're using OpenLDAP, with some customization using overlays. The on-line account management piece is tiny web application I wrote that provides a simple front-end for managing people's LDAP credentials. It just runs in Tomcat and needs the ability to connect to LDAP and an SMTP server.
Hope that helps,
Brent