While trying to connect to a Dell iDRAC 7 from OS X Mountain Lion with the Java 7 Runtime Environment installed you have probably received the very informative Connection failed error. Console.app shows nothing and you have to dig through ~/Library/Application\ Support/Oracle/Java/Deployment/log/ to find anything useful.
General consensus around the web is that you need to log in to your Dell iDRAC 7 from a Windows or Linux computer and then copy the trusted.certs file from %USERPROFILE%\AppData\LocalLow\Sun\Java\Deployment\Security on Windows or from ~/.icedtea/security/ on Linux to another directory. The trusted.certs file is not limited to Windows or Linux; it can just as easily be copied from ~/Library/Application\ Support/Oracle/Java/Deployment/security/ on OS X.
For whatever reason, Java 7 on OS X is not looking in the location above for the trusted.certs file; it is looking in ~/.java/deployment/security, which does not contain the trusted.certs file resulting in the Connection failed error.
To fix this, create a new directory structure in your home folder and copy the trusted.certs file to it with the following commands:
mkdir -p ~/.java/deployment/security cp ~/Library/Application\ Support/Oracle/Java/Deployment/security/trusted.certs ~/.java/deployment/security/
At this point, you can re-open the viewer.jnlp file and have console access to your server.
Unfortunately, Java 7 only allows 64-bit applications to be run. You will not be able to attach ISOs to the console through Virtual Media, which throws the Reason: The Virtual Media native library cannot be loaded error when trying to launch it.
I have tried browsing to the Dell iDRAC 7 with Safari in 32-bit mode.
I have tried adding this string to the resources section in the viewer.jnlp file, but I don't see a way to force the javaws command to use 32-bit mode.
Until Dell makes their Virtual Media connector 64-bit compatible, I am all out of options on OS X.
Update 2013-10-07: I have come across one comment stating that the certificate issue has been fixed in Dell iDRAC 7 firmware 1.37.00 and 1.40.40. I have been working with firmware 1.20.20. However, the Virtual Media connector still does not work in firmware 1.37.00 or 1.40.40.
Update 2014-01-17: I can confirm that the Virtual Media connector works after upgrading the iDRAC 7 firmware to 1.51.51.
Update 2014-05-31: Be sure to upgrade to the latest iDRAC 7 firmware because version 1.50.50 through 1.55.55 has a bug that causes the iDRAC to become unresponsive after 45 - 100 days of usage.