Should I add egg whites to my oats?

Krista J.
It really doesn't matter. I don't, it's actually the first time I'm hearing of that. Whatever works for you is fine. I highly doubt it changes anything.
Stay safe^
Love yourself~
Janusz U.
The short answer is YES, because it's giving you calories/macronutrients that last longer in your bloodstream than simple refined grains'. This will help most people feel satisfied and energized for longer.

Three long answer is it depends on what your body needs (check with a nutritionist), and your personal tastes.

I personally have low sodium and a high metabolism, so it's beneficial for me to include the yolk for the calories, sodium, and its extra nutrients as a bonus.

Others might not like the combined tastes of egg and oats, or may not be able to spare the extra calories in their diet, or may be on a low sodium diet.