Thems the rules though John, they are written in black and white and anyone can feel free to take a crack at it. You asked about the UFC, not the other organisations. The best in the UFC is not necessarily the best in the world, just the best in the UFC.
If there are no official rules for running a street car then there are no official world records. If there are rules for certain countries, and certain events.. then fine. You can be the fastest in that country given those rules, and the fastest at that event given those rules but you cannot claim to be the fastest in the world as other people in the world are restricted by different rules.
Edit: It would seem there may be a gap in the market here, a world class of street drag would be ideal.