If their moving, then the tremorsense makes it so that they are seen, but if still, then there are no tremors, therefore, they cant be seen.
Blindsight I would also rule as a form of tremorsense based on disturbances in the air,so, for those with higher senses then others would still note those who arn't moving, they would be breathing, their chests heaving, and both would disturb the air.
and if the argument is about the 50% miss chance, then to bad. The person stands in the block, the block covers their reach, Five Feat, and their foe prob also attacks with a Five Feat arc, therefore, when swining, unless the foe ducks, or jumps out of the way, then the attackers weapon covers all of the square where their foe was. If he moves, he is followed because of the tremors caused by his feat or his body if he dives away.