Well, if parents raised a procedural concern, no independent panel should allow its decision to be prejudiced in any way. (Of course, it's always a good idea to voice concerns in a courteous and reasonable manner.
If we're talking about the procedure leading up to the hearing, remember that it's the clerk who is responsible for making the arrangements, not the panel. (And the clerk must not influence the decision making.)
It depends what the concern is. Some procedural faults are little more than technicalities, whereas others can be more serious, leading to an injustice.
I can understand that parents would not want to give the impression of "nitpicking". The question they should ask themselves is "Have we really been put at a disadvantage?"
If, for example, parents had not been sent the case papers in sufficient time, and the authority's case is long and complicated, and there are documents that parents have not had sight of before, it would be reasonable to explain that there had not been an opportunity to study the papers properly. (In this situation, a chairman ought to offer an adjournment or a hearing at a later date.)