Is it permissible to publish a pre-print article on many sites, or is one sufficient? Do intellectual property rights allow this?
Arxiv's default license is a non-exclusive license to distribute the text: https://arxiv.org/licenses/nonexclusive-distrib/1.0/license.html
Obviously it does not prevent you from posting the text anywhere else. This is very different from what happens when you cede your rights to a publisher.
This may be limited by the rules of the various sites, but, so long as you retain copyright you can publish without violating "intellectual property" rights. Likewise if you give a broad license.
But, it seems sub-optimal to do so, since any citations made will be to the various sites, not to a single one.
Moreover, if you want to publish with a commercial publisher, you might close out your chances, since some of them want more control.