depends on what they take really; most of my comments or ideas are short things that are freely given for fun. It's the same with most people, if you planned on getting paid you should have done the video yourself, then you might have a leg to stand on with the complaint.
I've seen some youtubers however (cough tekking) regurgitate 2000 word essays and give the bare minimum of thoughts on them without even crediting the user. That seems pretty scummy.