First of all, good on you for taking such an interest in what your son is getting into. Aviation is tough industry to get a foothold in so being informed parents will greatly help his decision making process during training.
I have actually completed this course at UniSA so I can speak from first hand experience. It would be my STRONG advice for your son to save his money and time and stop doing the course to concentrate on flying lessons to a CPL standard and to get the theory exams done to ATPL level.
Unless the course structure has changed dramatically recently here is my reasoning-
The course does not see the student graduate with ANY CASA recognised qualifications. Yes it is a degree, but quite a useless one at that. (I will get to this later) By CASA recognised, I mean that NO theory exams required for a CPL or ATPL are sat while at uni. They are required to be studied for and sat outside of Uni time.
The degree itself is really not all that useful in todays industry. It is sort of a 'halfway' degree if you like. It is beneficial in enhancing your knowledge of aviation related subjects and DOES make sitting those exams easier, BUT the syllabus does not line up with the casa syllabus, so your son will still need to buy the usual textbooks that other non-uni pilots would have to buy to be able to sit the exams. I currently work for an RPT airline and have also been interviewed for some of the other major airlines in the country and not once has the fact that I have a Bachelor of Applied Science in Aviation come up. They are more interested in your Year 12 marks and flying experience. In fact depending on your son's age, it could be a disadvantage to stay at uni for 3 years. Airlines have what is called 'experience commensurate with age' (although this is less of an issue nowadays) where they assume an average flying experience to a set age. Normally a full time CPL course would take 12 months or so. If your son is already in his early 20's and completing a 3 year uni course, that is an extra 2 years he could be out in the industry working those first flying jobs.
Lastly, unless your last name is Murdoch or Packer, not finishing those last 2 years at uni will save your son circa $14k in HECS. At the moment that would pay for a Command Instrument Rating, which is done in a multi engine aircraft and is required before he can fly in Instrument weather conditions. Without this ticket his income will struggle to rise above $40,000 per year.
In terms of earning capacity in this industry, you are correct in assuming the lower end of the scale, but depending on his career progression and which companies he is employed by, expect him to be earning $30,000-$40,000 for probably the first 2 years, then when he is in a twin engine job $40,000-$50,000. To start earning anything remotely close to the median wage in Australia he will either need to be employed with a large GA operator or Regional Airline. Salaries at this level will start around the $50,000 mark and is normally reached 3-5 years after first getting a CPL.
Hope that helps.
Feel free to PM if you want further info.