Happy to report that on the newer X12 series with ASPEED IPMI, you can also use the iGPU alongside the KVM when you set the following options:
- "Advanced -> Chipset Configuration -> System Agent (SA) Configuration -> Graphics -> Primary video to PCI (this selects the ASPEED iKVM GPU as primary)
- "Advanced -> Chipset Configuration -> System Agent (SA) Configuration -> Graphic -> Internal Graphics to Enabled (this force enables the iGPU on the Intel CPU)
"Advanced -> Chipset Configuration -> System Agent (SA) Configuration -> Memory Configuration -> Max TOLUD" to "1GB" (2GB can also work, 3GB does not as it will hang in POST code 19)
Booting with this config will have all output on the VGA port as well as the KVM console. The iGPU shows up in the OS and can be used for HW acceleration even without any output connected. The TOLUD RAM setting does not seem to limit the usable video RAM for the i915 driver as I've seen it use well over 2GB with multiple vaapi encoding streams.
I'm using a fake EDID config in 1080p for a Xorg desktop session as well which i can live stream using HW acceleration.
Hope that helps someone