Is it permissible, Islamically, to profit from inviting others to register on file-hosting websites, knowing that the profits come as a percentage from the website's promotion, and not as a deduction from their earnings, and that the content of the files uploaded by registered users might be in violation of Islamic Sharia or copyright laws, given that there is no sharing of files between me and them?

It is permissible to upload files and earn money from them, provided that their content is permissible, and the website to which you upload them is legitimate and does not promote forbidden things. It is also permissible to publish links with the warning not to upload forbidden things, and whoever violates this, their sin is upon them. There is no harm in receiving a reward based on the number of entries via the link, as long as the money is not taken unjustly from people's rights.