Rafael,
I've looked into Interwoven from an architectural perspective in the past when putting together a content management solution for a client. That is to say I haven't done coding with it, but I reviewed all the docs about a year ago.
Most of the gig was about requirements gathering for the workflow and identifying technologies that would support them (internationalization, Akamaization, job/press release posting, etc.)
At the time, Interwoven had a pretty comprehensive perl/XML API for moving document template and content instances through a workflow. I suspect they're moving to Java now to keep the PHB's happy.
If I were to try to bolt the oACS on to it, I'd use the oACS server as a recipient of the Interwoven workflow and ignore it's CMS, perhaps writing a load script to import a new content instance into the oACS when Interwoven publishes/deploys it. It would get confusing I think to have two revision control systems, so I would delegate all that functionality to Interwoven where I suspect it works better. I would either ignore the file revisions in OpenACS by turning them off in the API or set up your import script to just keep overwriting the live copy.
Depending on your requirements, you might be able to skip the object repository entirely and just publish static HTML or ADP/tcl pairs. I remember that Interwoven didn't really distinguish between dynamic and static content... it claimed to be happy publishing either.
For the data backing the dynamic content (if any), there was a module to publish the latest version of a content database from staging to the production systems. I imagine it would be hard to get this to be happy with the OACS4.5 object model, and I'm not sure if they offer pG support, but it's something to consider.
As far as authentication goes, I think Interwoven could bolt on to OS accounts (*nix or Windows). You might want to consider using the LDAP module to keep them in synch, though I don't have major experience with LDAP/ActiveDirectory servers or the LDAP module so that might be wishful thinking.
Sorry if a lot of this comes down to: if I had more requirements I'd give you a better answer, but I hope the above is helpful.
