No, the Unit Indexer is required, although a Hashtable could be used as an alternative if you reworked the triggers slightly. I would recommend using the Unit Indexer though as it's arguably the most powerful and easy to use tool for making quick MUI effects. Note that you only want one Unit Indexer system in your map at a time though, so make sure you don't have copies of it.
Also, if you are manually setting the Custom Value of units in any of your triggers then you will run into problems. Luckily, it's very easy to adapt those triggers to instead use Integer array variables that take advantage of the Unit Indexer instead. A Unit Indexer essentially gives you infinite Custom Values per unit in the form of variable creation, and not only that, it doesn't limit you to just saving an Integer to a unit, you can save any variable type -> Special Effect, Item, Real, Point, Unit Group, etc...