I would be very surprised if actual hardware were required.
A driver that is just a driver will normally be accepted on its own merits with the assumption that there is hardware that it works on.
There could be a problem if you need to make changes to core-code to be able to support some aspect of the driver. You will probably be asked to show the driver that needs the functionality, but you might not want to finish of the driver depending on that functionality until you know it will be accepted.
In that case you need to open a dialogue, follow the "release-early, release often" principle (though maybe not too often) and risk the need to revise your driver if the core changes don't happen the way you hope.
Maybe the trickiest bit is know who to open the dialogue with in the first place...