There is an emacs plugin for directly editing a mail merge page in emacs:
http://code.google.com/p/confluence-el/
Is there something similar for VIM? I could not find anything.
Have you tried Vimfluence ? This is not a Vim plugin, but an external tool that loads a page, allows you to edit it, and then load it again. But he does the job.
It All Text! is a Firefox plugin that allows you to use any text editor to edit text fields.