Running VNC was not an option in my environment.
I switched from Exceed to XMing , I ran into many problems. Performance was one key area.
DBCA has some problems with the XServers , after the Finish Button is clicked at the end of the setup , the Database Configuration Assistance pops up. This was not possible for me in XMing.
I contacted a linux expert to understand the problem with XMing and he suggested that there may be some missing fonts. Even that did not help.
Later I switched to Cygwin
It seems to be stable as of now , DBCA works fine.
Here is what you have to do if you need Cygwin.
Download it and complete the setup.
Start a cygwin prompt
XServer pops out.
Open Putty and use X11 forwarding and connect to the server
Invoke xclock and it should be working.
I hope this helps.