The company I used to work for was a massive reseller of Barracuda kit, and as such I’ve deployed very large numbers of these units over the years (still got a decent collection of the free t-shirts you get in with each unit).
When setting up they basically sit as a smart-host infront of the server you wish to protect, so they will work with InterWorx (or anything else for that matter) no problem.
You can brand the entire system (including the messages users get about quarantined messages), and they will either generate each address (user) a set of credentials each time messages need action, or you can pull a user list in via LDAP or similar. You could probably write an InterWorx account sync plugin very easily.
The systems themselves are well built, and they’re easy to manage. They do a very good job at filtering, and will often handle much more mail than they advertise on the specs. The customer service and technical support that Barracuda offer is also second to none. If your business is going to rely on the box, I’d highly recommend their instant replacement plan if they still do it.
Hope this helps.