When the aboriginal Australians crossed to Sahul (Australia and New Guinea joined), there were already substantial challenges. Notably, significant sea distance (there would be parts of the journey in which land was not visible), and fast currents in the Lombok strait. In the 90s Australian archaeologists used to argue that the crossing (which would have required boat making and navigational skills) around 40-50 thousand years ago was the earliest example of modern human behaviour (there are now much earlier examples).

Mitochondrial DNA indicates that after that colonisation, there was no contact outside of Australia until well after other hominids were extinct.

Long story short, only H. Sapiens ever made it to Australia.

There were no traces of that seafaring culture by the time of European colonisation. So I would be suspicious of claims that there were oral traditions from hominids encountered before aboriginal colonisation.

Incidentally the remains of H.Floresiensis (the hobbit) were discovered on an excavation looking for evidence of the aboriginal journey to Sahul. The most recently dated specimens overlap with the arrival of H. Sapiens.

No, the first Australians and Neanderthals did not interact for the simple reason that there were no Neanderthals in Australia. The range of Neanderthals (as it is known from archaeological sites, tools and skeletal remains) is Europe, Western Asia, and Central Asia. So even though the last Neanderthals existed at the same time as the first Australians, they were in different parts of the world - the latest Neanderthal sites are in Spain and the Ural Mountains.

More to the point, the ancestors of Australian Aborigines were the first humans to migrate to Australia (and New Guinea, which was connected by land to Australia at the time). The earliest generally-accepted archaeological evidence is from 50,000 years ago, although there are disputed older sites. They are in turn descended from modern humans who first settled in Asia 70,000 years ago, and would have eventually reached what is now New Guinea and Australia by boat.

Now, as to whether those ancestors of Australians interacted with other humans, it gets a bit interesting. The hominid Homo erectus inhabited Asia for some 1.5 million years, and the youngest-dated remains are from about 50,000 - 500,000 years ago. That's obviously a big age range there, and so if the younger end of the range is correct then there might have been some overlap, but there isn't any evidence for this cohabitation one way or another.

Denisovans seem to be a different matter. Denisovans are a different species or subspecies of Homo (much like Neanderthals, this point gets debated), and they shared some physical similarities to Neanderthals, although they had larger molars. Denisovan remains are known from two sites - the eponymous site in the Altai Mountains of Siberia, and from a cave in northern China. Population genetic studies indicate that some 3-5% of DNA in modern Papuans and Australian Aborigines is Denisovan, so there is evidence of some admixture (although again, this wasn't something that happened in New Guinea or Australia), in a way similar to studies showing some degree of Neanderthal genes passed on to modern Europeans and Asians. So there was some interaction between these Denisovan humans and the ancestors of the first Australians, but beyond that we can't really say much. And since the arrival of the first Australians, native people in Australia have seen quite a great deal of change in terms of physical characteristics, material culture, and even environment over the last 50,000, so things have been far from static.

The Australian Museum has helpful information on the first Australians and archaeological evidence for them on their website, here.