I have a similar situation with a website I run. I asked the person that the site was about whether it could be dubbed 'official' but he said he preferred it as it was because it felt much more personal. I also guess there could be the issue that the person running the website could try and charge the object of the site for the pleasure so they may be wary about that! The best thing to do would be ask the band, and if they say yes, then all's well. If they'd prefer NOT to have an official fan site, then ask if you can have some contacts from them (PR
people, PA's, Agents etc) so at least if there are lots of other websites out there, yours will have all the information first off, and you'll receive loads of goodies to review etc!