This is not just about Urban Dictionary.
But - since it's crowdsourced -, a lot of people, if you ask.
"...Urban Dictionary averages 72 million impressions and 18 million unique readers."
"Anyone with either a Facebook or Gmail account can make a submission to the dictionary, and it has been stated that entries are reviewed by 20,000 volunteer editors."

Back to the writing of the name of Shakespeare:

William Shakespeare used the "Shakespeare" form in the first editions of the Venus and Adonis (1593), which is probably Shakespeare's first publication and he also used this form in The Rape of Lucrece (1594), which is currently considered as his second publication. This ("Shakespeare") form was the most common published form in Shakespeare's lifetime.

The form of "Shakespear" was used in the past (in the 18th century), but nowadays it is considered as a mis-spelling by most of the people.

The spelling of the name was later modernised, "Shakespear" gaining popular usage in the 18th century, which was largely replaced by "Shakspeare" from the late 18th through the early 19th century.

With rare exceptions, the spelling is now standardised in English-speaking countries as "Shakespeare".

I have got these quotes and the previously mentioned informations from the Wikipedia, which is also used by a lot of people (much more than Urban Dictionary).

Sources:
Spelling of Shakespeare's name - Wikipedia.
Urban Dictionary - Wikipedia.