You can upload video evidence to Imgur as well but you are not required to upload video evidence to only these two.
The only reason these two are recommended is because they are reliable and well known sites. Other sites might delete the evidence after some time or might have some bugs that make it difficult for others to see it.
Even though these two are recommended, u can use anything that you're comfortable with, even tho it'll have to be done at your own risk as you're responsible for the evidence u report with.