You mean
these racks.
For what it's worth, I use a Haulin' Colin porteur rack with a B&M Lumotec IQ premium light and I'm in Japan where traffic drives on the same side as in Australia and Britain.
I do get a shadow from the tire and fender and the side-mounted light, but it is not distracting. When riding at night you're usually looking 5 m or more ahead.
Though mounting the light on the side of the front wheel that faces oncoming traffic is preferable, I think it would work almost equally well on the offside because the cone of light is wide enough.