One update on this old topic.
I just have a DL360 G6 next to me and i experienced the same problem with virtual media. Apparently the solution in this case was to remove the internal usb drive because i also had a SD card installed.
My main goal/idea was to install ESXi on the internal usb drive and have a empty sd card plugged-in so in case the internal usb drive will ever "die" i can easy install esxi on the sd card (or the vice-versa) .
As soon as i removed the internal usb-drive , i managed to boot from virtual media.