Why are helmets not required on these vehicles - is there some sort of loophole where if you ride on the footpath you don't need a helmet ?

Absolutley no place for any of it in the workplace and I really like your question as to which is the most appropriate 'system' to use.
I dont want to sound simplistic but if you use an HSE system you may end up with a PG, but then if you use an HR system you may fail to manage a hazard - dammed if you do and dammed if you dont.
I'm inclined to agree with Andrew that it may be best not to have an HSE / OSH person involved as some (not all) may not have the sensitivity, empathy and other people skills that are necessary when dealing with such situations and may not have awareness of the HR requirements.
Provocative question - is it possible to seperate 'people and behaviour' out of OSH / HSE even though the behaviours have the potential to cause 'harm' which we do need to recognise as a hazard.
Broadly speaking the OSH / HSE view is that anyone could be affected by the identified hazard, but with sexual harrassment / bullying it is frequently specific to an individual.
Does having a SWM, JSA or PPE reduce or prevent injury from sexual harrassment or bullying ?perhaps the answer to that question gives a good indicator as to where the matterrest and what department is the most appropriate to manage the issue.

Well done Dianne Campton - you are the only one who mentioned going to the Sikh community and asking them for their perspective and possible workarounds.
The matter has never crossed my doorstep but I would be sitting down with those involved and their advisors to say A) this is what the work place wants - B) this is what you want - how can we reach an agreement. - Without discussing it with those concerned it may be that a balaclava type item could be worn that has a hard hat fitting on top - has anyone gone to the hard hat manufacturers and askedabout a Turban model ?
Lots of options yet to explore.

So this van is carring passengers on their way to work, gets remotely disabled and causes an accident or is involved in an accident where a passenger in the van is killed - is the driver culpable ?, is the person who imobilised the vehicle culpable and then of what - it would reasonably be manslaughter as their direct action caused a persons death - any opinions or comments - can we get the lid back on the can of worms ?

If the workplace is fully automated and people are removed from the workplace it will be incident free. Human error is one of the identifiers to the cause of any event minor to catastrophic and the eternal question WHY must be asked at every step of the way - in the case in question - WHY had he not used a lathe for several weeks, WHY was the job inappropriate for the lathe, Why was an energy drink being consumed ?
Lets run with the last one - was the employee tired - Why - is he working overtime Why - does he have a second job why - is he always thirsty why - is his attitude linked to something else why.
It may be that from the answers to these questions an unstable diabetic is identified who is not sleeping well as he is up every hour or so to the toilet, sugar levels are up and down which is why he needs the energy - SO human error may be the biggest contributing factor but once again ask why and look at what the employeer and employee are doing to maintain the health of the worker