Helvault has two activated abilities, both of which exile creatures. Exiling means to put a card into the exile zone. Creature that are exiled do not go to the graveyard and will not trigger relevant abilities that trigger when a creature dies (because ‘dies’ means ‘is put into a graveyard from the battlefield,’ and ‘exile’ is not a graveyard).

For example, if an Elder Cathar it exiled by one of Helvault’s abilities, the triggered ability of the Elder Cathar will not trigger. Similarly, if a creature is exiled by Helvault, the ability of Galvanic Juggernaut will not trigger.