Not sure what you mean by seamless? In my scenario, you update the WP blog and it’s there on the Rapidweaver site within the main navigation menu. No plug ins to depend on and no potential interface issues either now or down the line.
Keep in mind that stack products do come and go, and maybe for ‘API change’ reasons, sometimes stacks interfacing with other products are deprecated or fail to function fully. Such a scenario would leave you high and dry with hundreds of blogs to deal with. And of course, there is the issue of manually importing hundreds of blogs now. Yabdab’s plug in should show whatever you have currently but you will still need to maintain the WordPress blog going forward and hope that the stacks continue to be updated if/when required.
So your options seem to be:
Use RW blog or Poster Stack. Upside, plays nicely with RW. Downside, manual re-entering of hundreds of old posts required
Use CMS e.g. TotalCMS, Armadilllo, Pulse etc. Upside: plays nicely with RW, Downside: manual re-entering of hundreds of old posts required and still need an external, 3rd party plugin
WP on a Sub domain: Upside, dependant on nothing more than the existing WP blog. Downside: need to make it look like your RW pages