The Beat Movement was begun by Jack Kerouac, Allen Ginsberg, and William Burroughs. According to Jack Kerouac, the term "beat" was "describe both the negatives of his world and the positives of his responses to it."
Therefore, any piece (musical, artistic, or literary) which spoke/speaks to negatives in the world and the positive responses to it could be defined as containing "beat."
Almost all poetry, regardless of the movement to which it belongs, contains a beat. Songs also contain a beat, as created by the music. Art, as in all mediums which are used, can also contain a "beat," as defined by Kerouac's definition.
Furthermore, as defined by eNotes, anything which is "characterized by experimental styles and subjects, including spontaneous writing without regard for grammar, sexually explicit language, uninhibited discussion of personal experiences, and themes" could be defined as containing a "beat."
Therefore, when simply based upon the definitions provided, a work of art need not be part of the actual Beat Movement to be considered to contain a beat. It must only speak to the themes which were representative of the period: disillusionment, spontaneity, and social nonconformity.