Had the same problem but I came up with a solution. I start the jar manually using an old Java jre. It even works as a portable launcher! See the example at github.
I'm at the point of pounding the keyboard and tossing it across the room with not being able to get the Virtual Console to successfully connect. Here is the situation......   I'm able to access the iDRAC remotely via GUI or SSH and login and/or make changes without any issue. When I attempt to run the Virtual Console, it simply fails to connect. I get the error message in my Java Console of "Connection Failed". Now I've read other posts and recommended fixes and none of them had made any difference. Here is what I've done to date:  1) Added the DRAC IP into the Java Exception List 2) Changed the Java Network Setting from Browser to Direct Connect 3) Disabled Encrypted Video on the DRAC 4) Upgraded the Firmware to v2.85 5) Confirmed using tcpdump that my host and the DRAC can talk on port 5900 6) Cycled the DRAC Plug-in Type between Java and Native 7) Run the Virtual Console (viewer.jnlp) both through the browser and downloaded the .JNLP and used javaws on it.  I'm completely out of options and of what else I could do to make the Virtual Console connection stop failing. Does anybody have any other theories that might be causing me problems?
iDRAC6 Virtual Console (Connection Failed)