First check the publishers terms and conditions for posting on YouTube. Some don't even allow you to post videos at all, regardless of commercial or not. If it's clearly listed in the T&Cs that they allow monetising or commercial use, you are fine. Usually if YouTube require more information a link to these T&Cs are enough, but it depends on the person reviewing it. If you're unsure or in doubt, always get direct permission from the publishers, written permission. Save the email somewhere. When you send the email asking for permission, make sure you state which game it is for. They won't mind replying to you everytime you need permission either as most of them probably already get thousands a day and already have a reply email ready xD You can then copy and paste the email into the dialog box if YouTube ask for more information and if you saved it you can also attach the email for harder evidence (copy and pasting can look like you wrote it yourself).
