If all you’re using is Loot1Chance, then yes, 0 would mean don’t drop anything and > 0 would mean drop an item from this set.
If you also use Loot2Chance (and onward), then it takes the relative weights of the Loot sets to determine which one to dispense from, then taking under consideration the loot tables assigned within it (and their relative weights).
So as a simple example
Loot1Chance = 100;0;50;50;0
Loot2Chance = 0;50;50;25;0
Loot3Chance = 0;50;0;25;100
Item 1 = always from Loot Set 1
Item 2 = 50% of Loot Set 2 and 50% of Loot Set 3
Item 3 = 50% of Loot Set 1 and 50% of Loot Set 2
Item 4 = 50% of Loot Set 1, 25% of Loot Set 2 and 25% of Loot Set 3
Item 5 = always from Loot Set 3