Do Carbon Wheels Stay True Longer Than Aluminum Wheels?
I give you the following, that you can read here: 


  Talking to Jason Marsh the mechanic of Greg Minaar 2012 DH World Cup
  Champion about ENVE DH rims (which are carbon), he said that, ”Once
  you have built them, you don’t need to do anything, the spokes remain
  tight and they don’t need truing and we use a lot less through the
  year as they are stronger…”


The user in this forum reports long carbon wheel use with no need for truing, and DTSwiss also recommends the same maintenance interval for carbon and aluminium rims regarding checking if the wheels are true, which is an hint to them being similar.

The main problem with carbon, and this is also true for carbon components in general, is that despite being stronger than aluminium it is also more rigid, which means they don't respond as well to sharp impacts. Think of it as a steel vs an aluminium nail: the first one bends easily but holds the structure, while the steel one is very tough but breaks all of a sudden.

This is also said in this interview with a pro bike mechanic, that says carbon wheels are faster because you can maintain your direction better (more rigid), but have overall less durable because in an accident or impact they are more likely to require substitution. He even says that it is normal for costumers to try both types and prefer aluminum due to their compliancy and comfort.

Getting back to your question, I would say that due to the compliancy and flexibility of aluminium they hold dents and impacts better, as these are just killers for carbon rims. As the mechanic in the interview says, to which I agree, Carbon wheels are an expensive luxury. I personally would easily buy carbon components for my bike with the exception of the wheels, as these components in particular are very likely to have to sustain high impacts due to low tyre pressure, trying to go up a sidewalk or a bad measured bunny hop. We have all been there :)

Edit: You guys are right, I just threw it here :( I will try to improve.