Hi Bruce,
There has not been a thorough study of how rainfall events contribute to the spread of rabbit haemorrhagic disease (RHD), but it does seem very likely from circumstantial evidence. For example, following its initial spread from Wardang Island, RHD seemed to peter out over the summer, but it broke out again in central Victoria in late summer after localized heavy rainfall.
In the Flinders Ranges, I also recorded outbreaks of RHD immediately following heavy summer rains (50 mm or more).
The link with heavy rainfall could be two-fold. First, higher humidity is likely to favour flies as vectors (especially those big brown blowflies), furthermore, heavy rain in summer can stimulate rabbit breeding. Rabbits make more social contacts through mating, and fighting to establish breeding territories, and this no doubt helps the virus spread from rabbit to rabbit.
There is good evidence from live-trapped wild rabbits that they can be repeatedly infected with RHD. Rabbits that are seropositive, i.e., carry antibodies to RHD and have obviously recovered from RHD, show a boost in antibody levels from time to time and so must have been re-exposed to the disease. Whether they become highly infectious at such times is not clear, but like the common cold, or Covid-19, it is possible that the disease could continue to circulate at a low level even though most of the rabbit population carries antibodies.
As you suggest, the heavy rains in inland South Australia are likely to precipitate a mid-summer outbreak of RHD over a wide area.