Oh for cripes sake. I advocate guarded and confrontational thinking not necessarily behaviour, because it is by not thinking confrontationally that causes people to be bemused when they have been 'nice' and helpful and then they get tripped up by what they've said (eg I worked on one case where the question 'do you think that there could be any case where the same action could have been considered innocent?' asked in an informal and friendly pre-meeting chat, was answered with 'well I supposed if the situation was entirely different or between friends it could be seen as just horseplay' was used as grounds to drop the complaint because 'the complainant admitted that it could have been horseplay', and another where the employee had had no training when others had, and the question 'do you think your manager is very busy and could this be the reason instead' was answered ' yes it could be, because its hard for him at the moment but I still haven't had the right training' affected the decision 'because the employee admitted there was a valid reason for the manager not to provide training to her'. If the HR/employer becomes concilatory, then fine, but don't assume that being nice and problem solving first will encourage them to do the same in response.
By taking an action against another employee, no matter how justified, you are often seen, especially by naive and junior HR people who see the case first, as putting the organisation under threat - not because there is a real threat, but because any action is the first step on a road which can lead to public scruitiny, so they will need to be watching their step for a while. That doesn't mean you shouldn't raise grievances - in fact raising grievances regularly allows companies to freak out less when they get them.
If an investigation finds against you unfairly, pinning down unfair actions by the IO will help pressure those making the decision to change theirs, because a) it says 'you made a right decision, but the IO let you down' so allows them to be magnanamous, and b) because it will look bad at tribunal. That is all.
You don't have to raise it in a 'gotcha' way - but pointing out that this may be the source of the incorrect decision can be very helpful.
The fact that an IO will often see any challenge as an evil threat to the organisation is well understood, it is better psychologically to hold that view, rather than to assume that an honest and decent person has come up with a conclusion that feels unjust.
Understanding accepting and managing employer bias allows professionalism. (Rather than resignation) which is particularly needed when one may be going up against an organisation who wishes to hide problems. If the organisation gives warm and sensible signals, and is positive about grievances accept this, but be on guard until final outcome.
This is a much better strategy than being nice and getting shafted by heavy tactical players. I've been directed by an HR director to effectively push an argument towards polarisation away from conciliation in order to encourage action to be dropped so I do have experience in how tactics are played.
That said, this case sounds like it has been handled well (the 'consiliation' that there is no intent is an excellent way to soften HR/management faces, whilst still maintaining liability), so I am very hopeful.
As for the IO not being with the organisation - that means cross questioning and presentation of the case at any later stages could be difficult anyway so I expect employer settling the grievance early.