The remote Java KVM console on a Dell R710 server with an enterprise idrac works using the latest version of Java, thanks to MathieuW and the kind people on the below GitHub Gist

https://www.dell.com/community/Systems-Management-General/iDRAC6-Virtual-Console-Connection-Failed/td-p/5144021/page/2

https://gist.github.com/xbb/4fd651c2493ad9284dbcb827dc8886d6

Supported Platforms

Windows 7 x64 - Windows 10 x64
MacOS 10.9+
Debain/Ubuntu 64 bit