SSLv3 was deprecated starting with 131 of Java 8. This will cause connections to all iDrac 6 and earlier cards to fail, even if you're running the latest firmware. The workaround is to edit java.security on your machine.
(This appears to be reset each time you update java, so a simpler fix is often to simply keep an older version of java available and launch the jnlp with that version.)
Remove MD5:
jdk.certpath.disabledAlgorithms=MD2, RSA keySize < 1024...
jdk.tls.disabledAlgorithms=DH keySize < 768