We had the misfortune to have to attend a mediation where the other party brought along two lawyers, so we had to bring one too. That was a complete waste of time and money. It wasn’t covered by insurance.
It is difficult to answer your question without knowing what the mediation was about. Usually insurance doesn’t cover general legal costs, but it does cover specific instances including office bearers’ liability and OHS claims. As Jimmy said, an insurer may make a smaller one-off payment, but that can contribute to higher premiums.
There should be something in the EC minutes re the mediation, as the EC has to resolve to attend the mediation and those attending have to be authorised to agree to whatever is agreed there.
I am not so sure reimbursement of legal costs would be accounted for as revenue.