It's not that their SR-IOV implementations are incompatible, it's more that SR-IOV doesn't imply anything about driver compatibility. It's is a mechanism for exposing underlying hardware (or slices of hardware) to guests and nothing more. It does not encompass register sets, queue formats, etc.

So you can assign a virtual function from any SR-IOV-capable NIC into a VM using common code, but what the guest sees inside the VM will still be an Intel, Mellanox, Chelsio, etc. device. Naturally they'll need a driver for that device.

If your fleet includes NICs from a variety of vendors, you'd never be able to live migrate VMs between hosts with different NIC models. Until recently, no vendor I knew of included the relevant serialization and deserialization functionality to allow for live migration at all.

Good point. I didn't think of the driver incompatibility between vendors.