It is my understanding that the owner of a home built RAAus aircraft must be the builder to be able to train in it. (Refer CAO 95.55 para6.2 below). This is not the case for GA, training is restricted to the owner with no mention that they need to be the builder. I can't see why there should be that difference.
CAO 95.55 para 6.2 In spite of sub-subparagraph 6.1 (a) (ii), if a person has wholly built or assembled an aeroplane to which this Order applies, or a group of persons has wholly built or assembled such an aeroplane, then that person, or each of those persons, may use the aeroplane for their personal flying training.