Although it's not said specifically that it is supposed to be THE Freddie Mercury, the character looks very very much like freddie, he is a singer and goes around with his own theme song, and his name is freddie. Also, the first volume of the show is titled Cromartie Rhapsody and the characters on the box are in the classic Bohemian Rhapsody pose.

For a look at the box cover and reviews of the show check out

http://www.animeboredom.co.uk/anime-reviews/cromartie-high-school/539/

or just do a search for Cromartie Highschool