Chambers Dictionary suggests it may be from the dialect word 'mullethead' meaning 'fool'. Perhaps that was on the basis that the hairstyle may have been considered somewhat foolish!
The Sunday Mirror obviously agrees with you as to the 'dodginess' of the mullet. Here's a quote from a 1998 edition, "The mullet...if you have one, then a word in your ear: Scissors."
In American English, a mullethead is a flat-headed fish and here's a quote from there in an edition of Harper's Magazine published in the 1860s about it, "Dat fish is a mullet-head; it hain't got any brains."
Seems the idea of daftness regarding the mullet exists on either side of the Atlantic!
Nice theory, but unfortunately drum predates drum 'n' bass by a couple of centuries. Eric Partridge suggested it was of Romany derivation: scroll down to 'Home sweet whatchamacallit' here for a discussion
Further to QM's answer, and for your info and entertainment, Chambers defines mullet as: "a hairstyle that is short at the front, long at the back, and ridiculous all round".