There's no forum for widget/theme developers.
It looks like there used to be one, because dev.netvies.com has a link to http://dev.netvibes.com/forum. But that just redirects to the blog.
Why would you not want to encourage communication for developers trying to expand the content on your site?
I'm interested in creating some useful widgets, but the removal of things like this give me the impression that netvibes widget development is dead.