Old rules die hard. Nationally it was not permitted to double count hours. The 10 hours referred to in the FI prerequisites is the same 10 hours that are included in the CPL and IR courses and which can be credited to either course. The hours from the PPL would not be credited to hours on another course, but as you say the regulation doesn't specifically prohibit it and the 10 hours need not be part of a course however; if you intend to go on to the CPL and or IR it might be an idea to obtain experience that can be credited to those requirements. In any event the ATO conducting the FI training will determine what is and isn't acceptable.