Well, DDG is owned by Yahoo... Also, it is not open source completely. So you cannot know if it is really tracking you or not.
And duckduckgo is not owned by yahoo. It has partnerships with yahoo, bing and yandex to use their search databases.
I am not sure that partnership or ownership really changes anything. But I hope I am wrong about it. :)
It changes everything. DDG is a Yahoo customer and, as adrusi wrote, sources search data from them among other providers. Yahoo doesn't control DDG, its privacy measures, data collection, or product direction as they would as a parent company. The relationship is completely different.
I do agree with you about Searx having the optional self-hosting advantage. DDG claim they won't track you, but there's really no way to be certain.