First, a disclaimer: I just started installing my first UC320W today; however, I've had a decent amount of experience with enterprise telephony and analog integrations.
That said, I'm not sure how well the plain paging output on the UC320W will integrate with your Bogen system. Since the output provided by the UC320W is "audio only" I'm unclear as to the Bogen needs to be configured to initiate the page. AUX port maybe? In my (enterprise) experience we've always preferred FXO then FXS as the preferred paging adaptor types so I've never gone the plain audio route myself.
I'm curious to hear what other people have to say though. The UC320W has a dedicated paging port out there and the UTI-1 has every feature a phone guy could want in a paging adaptor so I'm sure the two can work together somehow. I'd give Bogen a call - (in my experience) their sales guys are really helpful in validating proposed designs for you.