Not at the moment. There's been a lot of interest in a jFusion plugin, but so far the only developer that has offered services wants to be paid up front instead of using an escrow or freelancer site, which the various admins object to.
There's a good chance that jFusion's universal plugin may be able to deal with it though...
jFusion bridges multiple different software packages with Joomla!. They've abstracted all the infrastructure required for a bridge, so all you need is a "Plugin" for jFusion (jFusion is a Joomla! extension), and you can then bridge your Joomla! system with whatever the new plugin is for. It can link together multiple packages, provides single sign on, singe registration and can handle visual integration etc. You designate *which* of the software packages is the accounts DB master or if Joomla! is.
Take a look at it if you're running Joomla! www.jfusion.org, it's a great OS project free to use though donations are greatly appreciated. Most of the plugins are built and maintained by developers that use them for their own sites and/or software. They have a great forum with resources for developers etc.
Last I looked they had plugins for: : phpBB 3, SMF 1.1.x, vBulletin, MyBB 1.4, Magento, Moodle,DokuWiki, Gallery 2, osCommerce & Clones, eFront, Wordpress
I was able to get Joomla/Xenforo bridge working and users synced using the guides here and here. However, users can't logout, and other strange errors. I think it's because XenForo registration is Enabled. Does anyone know how to disable registration from xenforo?