No, that code isn't necessary because Muse exports HTML5.
The doctype you've posted there is for XHTML Transitional.
Here's more information about the various doctypes: http://www.w3schools.com/tags/tag_doctype.asp
But remember, Muse takes care of the code for you, so you should never need to add a doctype to your pages.
Best regards,
Corey
