Hi Pete.
We've had the occasional one. Last year of note with Pre-TC George that was deepending over darwin on its way to WA. It produced a supercell which spawned an EF2 perhaps EF3 tornado in Kakadu National Park - I've posted a thread about that in the forum. Caused some damage to outback home and car trailer, with several trees down. There was a damage path also.
They do occur with depressions and cyclones, in fact most hurricanes per se can develop tornadoes once they reach landfall due to rain bands with large cells embedded and strong shear associated with them.
There's some dispute at the moment whether the NT holds some kind of tornado frequency in this country - and yes I'm fully aware of what that state is people and it aint here!!! We don't have the conditions to support supercellular activity unless provided for by tropical cyclones or depressions. There's not enough helicity/shear/vorticity during even severe TS's. We get a few water spouts from strong updraughts in some storms, mostly unseen.
The argument raging here between some folk is that because they may be unseen or unreported due to our expanse of uninhabited land that there may be more than what's actually known and that dry line supercellular storms actually do exist here due to the separation of a desert and the tropics - a dry line.
For me I stand by the simple fact that we don't get 'dry line' storms - in the actual sense of the meaning. Anyone can get storms 'on a dry line' but not the type that most seasoned/experienced chasers have seen and usually they're supercells. I've looked up every available online info article on tropical storms and yes, they can form on dry lines, BUT they are not 'dry line' storms in essence of being supercellular.
I quoted an article to some folk by Tim Marshall, a well-known and respected chaser/meteorologist with the SPC and NSL on such matters - even that did not change the minds of a few - goodness sake, they did not even believe him!
...another thread perhaps on this topic - in fact I'll start one. I'd like a few answers and there's plenty of resource bodies on this forum to give it.
But, yes. We get the odd one with monsoonal lows only if the right conditions prevail.
Mike