i think having a youtube channel videos helps your x factor chances with the auditions and also getting noticed, but it is probably not essential, i know when it comes to the televised auditions rounds, before the act goes before the real judges they sometimes show some clips from there youtube channel if they have one.
and also if you decide to do a video audition/submission and upload a video to the x factor applications form, you could probably also list your youtube channel for them to check some more of your singing, if your channel is really good that is, otherwise best to just upload one video auditions submission with the application form and leave it at that.
where it can also help with auditions after having uploaded videos to youtube with your singing, one you will be more confident with auditioning in a video format, so when it does come to uploading a video audition to the x factor website, you will find it much more easier and more natural if you have had some practice and got used to doing singing videos.
and you might also find it helps as well with a real life audition that you would do if you went to one of the open call x factor audition venues and tried out, because even though that is auditioning in person, having done some time making youtube videos this would of helped your confidence and been lots of practice for auditioning in person, though not essential by any means i think a youtube channel could help some people improve there x factor auditions.
though you do not need modern technology to practice singing or auditioning either, because it can be good to just sing natural or looking in a mirror or out into space.