The effect is cumulative. Human creatures you control will enter the battlefield with a +1/+1 counter for each Dearly Departed in your graveyard.

In most cases, when determining whether a creature entering the battlefield under your control should get a +1/+1 counter, you'll simply look at what the creature will look like on the battlefield. You'll consider any effects affecting a creature entering the battlefield under your control that fall under one of these categories: --Replacement effects that have already modified how the permanent enters the battlefield, like the one created by Clone. --Continuous effects that changed the permanent's creature type on the stack, like the one created by Artificial Evolution. --Effects from the permanent's own static abilities, as long as they affect only that permanent, like Adaptive Automaton's.

However, you’ll ignore the continuous effects of static abilities that come from other sources. For example, if you control Xenograft with Human as the chosen creature type, a Vampire creature would not enter the battlefield with a +1/+1 counter.