I think most common law jurisdictions would accept the report of a Royal Commission as of persuasive value, but testimony at an RC is of limited value as evidence. A witnesses own statement cannot be used as evidence against them, for instance. This is covered by the Royal Commissions Act 1902.
JC notes and records being child pornography is an interesting thought.
According to the current law in Queensland where I think this JC was heard (Edit: BCB's case was actually in Western Australia. But the law in all jurisdictions is similar enough that the general points are still valid):
child exploitation material means material that, in a way
likely to cause offence to a reasonable adult, describes or
depicts someone who is, or apparently is, a child under
16 years—
(a) in a sexual context, including for example, engaging in a
sexual activity; or
(b) in an offensive or demeaning context; or
(c) being subjected to abuse, cruelty or torture.
So, possibly needlessly explicit notes about abuse and cruelty might fit the definition. Although I doubt the proceedings of a church hearing was the sort of material the Parliament would had in mind when the legislation was considered.
But is there a defence to a charge of making, distributing or possessing such material in the case of a JC?
228E Defences for ss 228A–228D
‘(1) Subsections (2), (3) and (5) prescribe defences available to a
person charged with an offence against section 228A, 228B,
228C or 228D.
‘(2) It is a defence for the person to prove that—
(a) the person engaged in the conduct that is alleged to
constitute the offence for a genuine artistic, educational,
legal, medical, scientific or public benefit purpose; and
(b) the person’s conduct was, in the circumstances,
reasonable for that purpose.
Example of something made for a ‘public benefit’—
A current affairs television program showing children being tortured
during a civil war.
I think it would come down to whether a reasonable person would think the material was too detailed for a legitimate church disciplinary purpose and that a paedophile would get off reading it.