I was able to pass the card through to a Linux VM running ubuntu 20.04 and it shows 1G but I can almost get 10G through it with iperf. I was hoping to be able have the card show up as vmnics.
Glad to hear it worked.
The AR8151 network chip is actually a 1GB chip, but the virtual chip as emulated by the CCR2004-1G-2XS-PCIe
also provides 10GB and 25GB speeds. The adapter name displayed in Linux still is "AR8151 v2.0 Gigabit Ethernet", same for the link speeds, what is a bit confusing.
To have it working as a real "vmnic" wrappable by the VMXNET3 pseudo driver and available to all guests, ESXi would require a native driver. This is unlikely to ever happen, except MT creates one.
The CCR2004-1G-2XS-PCIe specs could do a much better job with indicating the emulated NICs in passthrough mode only work in Linux. Either on a real box, or by passing it into a single guest for exclusive usage.