I have more than 100 D1800 boards running on my farms, and I upgraded their BIOSes days ago.
there are 3 BIOSes which you can download from their official website, the latest one is actually the VGA-display-only one, whatever kind of cards you plug on it, it will always output the signal by VGA, you should try it and it works like charm with KVM.
My rigs are on P104-100, P106-100, 5704, 5708, all of them are running perfectly with it.
Sorry for no support website in English.
http://www.onda.cn/MotherBoard_Supports.aspx?id=369P.S. 3 BIOSes:
"默认打开PXE ROM 选项，修正WIN PE 兼容" means "opened PXE ROM option by default, fixed compatibility with WIN PE"
"更正上专业矿卡/带输出矿卡，板载VGA 无输出状况.更正上UEFI PXE 无盘，无法进系统问题。" means "fixed if video card installed/not installed, VGA doesn't work , fixed if no disk found in UEFI PXE, system halt." <-- I think this is the problem you met.
"修正和VEGA SERIES 显卡兼容性问题" means fixed compatibility with VEGA series cards