Is there an XMPP (Jabber) client for Android that supports video calling? I have searched quite a bit but still javen't manged to find a general Jabber client that supports video calling. There are a few that support sending video files though.
No there is no federated XMPP Client for Android that supports video calling. Federated because there many proprietary XMPP Clients that do so, but they work only within their own network.

The reason because there is no such XMPP client is pretty simple: Jingle (the XEP which is used for XMPP video calling), is pretty new and most XMPP libraries don't support it yet. This is especially true for the most relevant XMPP library Smack (relevant because it's a Java library). Smack has some Jingle components, but the development on them stopped years ago and they don't seem up to date.

Update: Jingle development in Smack gained some traction in the last months.