A lot of popular books about ADHD convey the idea that adults with ADHD combined type tend to have low esteem. I'd say it's probably more accurate to say their self-esteem fluctuates. Sometimes their self-esteem crashes after they make big impulsive mistakes, but much of the time they have plenty of self-esteem.
For a start, they tend to be over-represented in work fields like sales and marketing where having a robust ego goes with the territory. If you're timid and self-effacing, then you aren't likely to be a big success in sales.
One of the one famous people believed to have had ADHD combined type was the British Prime Minister Winston Churchill. Having studied the guy at university, I can tell you that he didn't suffer from low self-esteem. If anything, he often overrated his own abilities, and he made a number of over-confident (perhaps impulsive) decisions that turned out badly. For example, he frequently went against the advice of military specialists and got Britain involved in two disastrous military campaigns in Turkey and Norway.
If Churchill suffered from a lack of self-esteem, then it's more likely he would have been criticised for being too indecisive.
It's likely that low-esteem is more common among those with inattentive ADHD. People with people with this form of the disorder, tend to have higher anxiety levels and more have more self-effacing personalities. However, even with this form of ADHD I don't think low-esteem is a particularly big issue.