You can't have check and training approval until you are trained to that level on the appropriate category of aircraft buy your airline, and issued an Airline Flight Examiner Rating. So there are few parallels to be drawn with ab-initio instruction. In NZ to be a training captain under Part 125 (medium aeroplanes) you need an A, B or D Cat Instructor rating so it can be an advantage to have one of these going into it, but certainly not manditory as the airline is able to issue a D Cat.
Instructing hours are certainly not a waste of time, particularly Multi IFR instructing - airlines usually find that new hires from an istructing background have better legal and proceedural groundings than ex charter pilots. If that is the attitude in Australia, it is certainly not mirrored here.
Chadzat, that's fine in a perfect world, but as Aussie pointed out most instructors are there to build hours - as you say though, they do need to be focused and proffesional or it's not fair on the student.