It is important to distinguish between the (the software that randomizes) and the ROM (the game file itself).
To understand the "Emerald ROM for Randomizer," one must first understand the concept of a Randomizer. A Randomizer is a third-party software application that takes a standard Pokémon game file (a ROM) and shuffles its internal data.
If you've played through standard Pokémon Emerald multiple times, a randomizer breatses incredible new life into it. Using a clean, standard ROM with the Universal Pokémon Randomizer is a match made in heaven.