hi !
to me, all kind of musics as reggae, rock'n roll, blues and ragtime are nouns
They may be adjectives if you add the word music : ragtime music and even there to me it's a more a nominal group......
Nowadays , you don't have to say I play rock'n roll music , but just "rock'n roll"
Besides the ragtime was a musical style which began in the late 19th century......
In my opinion it's a noun !!!
Bye !! hope I helped .......