No you could not use it commercially, unless your license is from Paramount (or whomever owns the rights to designs from Alien).  If you aren't working on the next Alien sequel, why would you want to use their design in your commercial project anyway?  If I saw an X-Wing in Battlestar Galactica I would think it odd.  As for getting the free one versus the pay one, why do some people buy bottled water and some collect rainwater in buckets?