Do Scavenger Trinkets stack in co-op Orcs Must Die 2?

Solution 1:

According to a Robot Entertainment employee:

A little trinket design heads up.

Trinket passives apply to the owning player only while the active effect apply to both the owning and the coop player.

Example: The healing trinket only passively grants regeneration to the player that equips it but activating it will heal himself and their coop partner.

I did find a specific mention of the scavenger trinket having a unique property:

All Trinket Passives apply provided they are in your loadout, and only for you not your co-op partner. The only exception is Scavenger, So long as one of your traps added a combo point scavenger applies its passive effect even if the killing blow was dealt by your co-op partner.

All Trinket Active effects apply to both players.

Source: Robot Entertainment Forums

Source: Scavenger Trinket Passive

Solution 2:

The active ability of the Scavenger Trinket mostly stacks in co-op play. If only one player has the active ability activated, both players benefit from it. If both players have the Trinket activated at the same time, however, only the host gains the benefits of both Trinkets (the other player continues gaining only the benefits of a single Trinket activation).