Use of the Jabber/Jabber Guest SDKs from within embedded browser components is unfortunately not supported.
Currently about the only option for integrating a Windows native app with CUCM video is via SIP - however Cisco does not provide/recommend a SIP stack or RTP/media handling stack, so this is a pretty heavy lift.
I do understand that a C# library for Cisco Spark SDK video is in the works - which would address your need (though via Spark, not Jabber), but no ETA quite yet...