It shouldnt be a problem. Ive put a disclaimer on all the pages plus sega even have a section on their website where you can send them your sonic fansites and they put the best ones in their sonic central every month or so.
I have emailed sega now for confirmation that they do not mind (maybe I should have done this sooner and will see what they say).. If they mind ill follow any directions they give.
Thanks for telling me so I can get this sorted before I do get into trouble
UPDATE:::
Ive spoken to the Admin on the official sega forum (so he works for sega im guessing) and he said so long as you put a disclaimer on the site and dont claim to be sega there have never been any problems.
Still waiting for an official email from sega but for the moment it seems there shouldnt be a problem.