multiple domains point to same site on WP-MU

If they’re just to get visitors there and you don’t care about making the site “look like” the alias domains, you can just 301 redirect the site using .htaccess or similar. If instead you want to make it “look like” visitors are on the alias domains then you may need to work with your host to figure out how to mask the URLs. Keep in mind this may have negative consequences for SEO so unless you absolutely must mask things, it’s probably better to redirect instead.