Hel was able to figure them out with all of 3 days to make the plan. That does not suggest that the problem is particularly obscure or difficult to predict.
Heck, theyre even aware of the possibility of outsiders screwing with the vote, because they have a barrier meant to stop non-dwarves from getting in, as well as a security team. Is it that hard for the cleric of Dvalin to cast a circle of protection from evil around the table before the vote goes off to make sure nobody has their free will violated?
As for your example, allowing people to override the free will of the representative if they think theyre voting wrong defeats the whole point of having a representative, to say nothing of being highly immoral. If thats the concern, pick somebody who will actually represent the interests of your group.