Position seem plausible. As for fauna/flora,Denton would definitely have connection with Australia. I am sure that Denton would have it own subspecies (or even species) of marsupials (kangaroo, wallabies, possums, opposums, wombats etc), if it was connected with Australia in the past. For figure out this, the movement of lithosphere in Indian Ocean would give the answer.
According to an animal encyclopedia I have, and a distance from Australia of ~300 miles (~550km) Denton would have (supposing that it was always an island, never connected with Australia):
-Tortoises (they can travel >800km, look Galapagos tortoises)
-Reptiles (snakes, lizards etc), these can travel >800km also
-Anything that flies (birds, bats etc). If there are no marsupials or other large land animals, Denton may had moa like New Zealand or a similar species.
-Insects, amphibians, land mollusc (>3200km).
As you see from above, Denton would definitely have snakes. Some will be poisonous, so Dentonites would learn to live with them!
Also, there are two categories of Islands : Continental Islands (which were part of a larger mass and broke out, still connected bathycentric) and volcanic/atolls (which were created by other forces).
Seeing the South of Australia, which is like an arc, I think that Denton should have a similar shape, as it was part of Australia which broke out somehow. Here is a link for lithospheric plates and their movements:
http://www.coa.edu/stodd/oceanweb/ocean ... sld026.htm