is it alright to host libdvdcss package in COPR or should it be deleted? (more info here: https://www.videolan.org/legal.html).

The licence is ok (GPL) and it's not listed here: https://fedoraproject.org/wiki/Forbidden_items

But I am not sure if it goes well with US regulations.

See COPR specific regulations here: https://docs.pagure.org/copr.copr/user_documentation.html#what-i-can-build-in-copr

Thank you
Michal Novotny