not sure if I understand the question, but all you have to do is make a link to your vb install (and viceversa) and you can skin your VB install likeyour WP theme if needed, which is quite easy if you know what you're doing.
Now, if your question is if they can share databases and tech stuff like that, yes, it can be done, but it's really complex and painful, at least if you want it well done. However, what you'll be charged for this might be really expensive, 4 figures for sure
then again, not sure if I'm understanding your question correctly