Vanoss and other Youtubers are great at making their own thumbnails typically using Photoshop and Illustrator.
I think it's better to make your own thumbnails, I understand some Youtubers who put out a lot of content probably have their hands full so they commission them out to someone, but I don't like the idea of someone else making my thumbnails.
I think it's beneficial to have the skill to make them yourself, and I wouldn't really use software that makes thumbnails, it all sounds a little tacky.
Beastby