I have upgraded the KVM firmware, which upgrades the KVM dongles as well with the same results.
I would agree that the KVM is the issue, except that we are running another DL380G5 on the same KVM without issues.
The KVM only has VGA ports, no DVI.
I have checked the BIOS in the past for reference to the VGA port, but I have not found anything relevant.
An external monitor works fine on either the front or rear VGA ports. The KVM dongle can only plug in to the rear VGA port (it gets power from the PS/2 ports).
I suspected it could be a refresh rate mismatch, but the BIOS has no setting that I can find regarding VGA refresh rates. (The no video occurs all the time, there is no POST displayed when on the KVM, but there is when using an external monitor)