Should be BusNumber e.g.
I understood the bus number to be the controller number. This is what the VMStudio documentation states
rasd:BusNumber– The controller number. Controller 0 on hard drive 0 is defined to be the boot device.Four controllers are supported (0‐3). This doesn't talk about whether the bus sharing is physical or virtual.
It doesn't appear to be a way at the moment (that I'm aware of). Although, it is possible there is a specific property on ESX which I am personally not aware of that could be supplied. I will see if I can find someone who is more familiar with it.
The other alternative is through the client settings:
Adding the following to the ovf file along with config for pvscsi controller, the pvscsi controller gets created in shared mode.
<vmw:Config ovf:required="false" vmw:key="sharedBus" vmw:value="virtualSharing" />