Not required but preferred. Rememberm you can get your WP blog in the search engines using wordpress's free set up.
However, doing this approach really leaves you limited as to what you can do with your blog. It is always best to go with hosting your own WP blog on your own hosting provider, so that you can advertise affiliate programs, and put the type of content and promotions freely on your WP blog without restrictions.
That said, either approach of setting up your WP blog should get you listed on google all the same.
Hope my answer helps!