IF the substance of the email in question as well as the response to it are to be taken as true then it speaks volumes about the workplace culture of this particular organisation - which is being frequently reported in a somewhat unsavoury light.
In a high stress, high performance and hazardous environment bullying and any behaviours that add to the stress load of instructors is potentially lethal, can and will seriously damage your brand and reputation.
ANYONE who fosters and facilitates such an environment is, in my view, culpable for any negative outcomes that come about - for firstly not creating a means for personnel to air their grievances and for failing to emphasise HR policy on workplace bullying.
I have a great deal of experience with corporate governance, HR policies as well as Safety Management Systems and the just culture element that is meant to underpin their use. Unless there is evidence of repeated negligence as per a written policy statement in your ops manual aligned with annual performance KPIs set at the beginning of each year, there is NO dotted or hard reporting line between HR the Safety Manager and the HOO.
It's advisable to submit senior personnel in leadership roles such as HOO/Dep HOO and Safety manager for appropriate training and ensure that ALL personnel are on-boarded and understand that there are appropriate standards of behaviour that are expected in any Australian workplace. Anyone breaching these standards needs to be counselled and as necessary disciplined. Not doing so opens you and your organisation up to potential legal consequences and worse - people have died in workplaces as a result of workplace bullying and personally I have no patience for it. If employees lash out in anonymous forums then perhaps the issue is not with the accuser but rather with an environment in which they don't feel confident in airing their grievances and being heard - isn't that the essence of the Aussie fair go?