Hey Dazza,
If you have not seen our Worldbook for The Hunt: Rise of Evil yet we did much the same thing. We feature Freeport (from GR) just outside our pirate clan nation called Sheena, We feature Bluffside (from TG) in the nation of Kirkland, We used the Seas of Blood supplement from Mongoose for our seafaring rules with an excerpt and examples using the OGC.
We even dedicated a half page to mentioning other books from these fine companies that would be a good fit. This book got into retail stores a few weeks ago but was late getting out for review.
The bottom line is if you need a new world and pick up our Worldbook you automatically have two fully fleshed out cities, Sea rules already in place, and our other books that are out and forthcoming. This makes it a very well supported setting and easy to get started in. My greatest hope is that by doing things like this we create a synergy of sales and support that will help both consumers and publishers alike.
Oh yeah, In our upcoming release, UrbanBlight, we are using the half-Ogre Template from Bastion Press that appears in Minions in addition to some other good OGC from 3rd party guys. Jim Butler was very kind about our use of that material. Yes, I know it is OGC but as a fellow publisher I always ask.
Also, Dazza, drop me a line some time. I have not heard from ya in a bit and like to keep in touch with happenings down under. I am not sure if you remember me telling you but I lived in Bondi Beach for about a year and would love to come back to Aussie land at some point.