If the plugin doesn't handle it in an additive manner, it won't be compatible with any other yield increasing plugins if its loaded before your loot manager plugin.
There are 2 ways a plugin can handle it:
a) The plugin SETS the multiplied value. For example if you would normally gather 25 wood, and the plugin is going to change it to 3x, it would set it to 75 wood. This is bad because any plugin that modified it's value is rendered completely useless, as its override entirely when the new plugin SETS the value.
Example: SkillTree sees the default 25, works out the player has a 100% boost, and applies an additional 25 wood onto the stack, bringing us to a total of 50 wood. The loot manager then takes priority and SETS the item.amount to 75, nullifying what SkillTree did.
b) The plugin ADDS the additional multiplied value. Rather than setting the item.amount to the new value, it simply calculates the difference between where it needs to be (75 - 25) and adds the difference (50). This means that any other plugin that may have handled the item.amount field before this plugin gets to it will still add their values on top of it.
Example: SkillTree sees the default 25, works out the player has a 100% boost, and applies an additional 25 wood onto the stack, bringing us to a total of 50 wood. The loot manager then takes priority and ADDS 50 to the item.amount (75-25), bringing us to a total of 100 wood. This means that both plugins were able to add their values.
Option b should be the way that any plugin handles the value, unless it fires off before the oxide hook (using Harmony).