I am using the same motherboard with bios v1.03. The on-board VGA works just fine with Tesla C1060 and GeForce cards as well - using the driver v190.53. I didn’t have to flash the VBIOS either but as far as I remember the documentation mentions something about this being necessary in some cases.
When using GeForce cards I had to fiddle a bit with the xorg.conf, but is definitely possible to make it work. To force the OS to use the ASPEED this is my Device section:
and in the Screen section I manually select the device, monitor and also the mode defined in the Monitor section:
HorizSync 30.0 - 81.0
VertRefresh 56.0 - 76.0
ModeLine "1280x1024@60" 135.0 1280 1328 1440 1688 1024 1025 1028 1066 +hsync +vsync
Viewport 0 0
Note that the ModeLine is specific to the monitor so you need to look up the correct values for your monitor.
When using only Tesla cards, as the on-board one is the only VGA adapter X does not get confused and everything works without fiddling with manual xorg.conf tweaking.