I think 'gulag' is used either to refer specifically to the Soviet camp system, or is used metaphorically in reference to some other camp system, in order to emphasize a similarity with the Soviet system. So I don't think there is any need for two articles, since the word and the acronym have the same referent. And to fall back on convention, the book 'The Gulag Archipelego' is always spelled with 'Gulag' the word, not 'GULAG' the acronym - suggesting that the word is correct even when referring specifically to the system. - Tim