I dont think its accessible in Emerald,but in Ruby/Sapphire that room was where you went to battle trainers that you scanned into the game with the Battle E-cards(y using the Gameboy Advance E-Reader)
but to date I havnt yet discovered how to get any items(other than the Eon ticket w/ E-cards in pokemon emerald)
hope I helped!
~Engel der Bosheit
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