Smogon's community was divided between implementing every in-game mechanic in their simulator. In-game mechanics include EVs, moves, accuracy and even glitches. This "issue" escalated when the admins felt divided on how they should continue with the simulator. A poll was held in which it was decided that Smogon need not follow all battle functions. This effectively meant that most glitches which were in the original games were not implemented vis-a-vis the new policy.
This affected the Acid Rain glitch too. It was removed from the official Gen 4 competitive. Smogon doesn't apply it to their formats. Showdown doesn't venture into the grey areas of mechanics which can crash/endlessly loop the game. However, it's optional and players can add it to their battles. (If in case it leads to an endless loop, the battle would be a forcetie.)
(Note that a few formats in fact do have this glitch applied, like Gen 4 Pure Hackmons. Other than Hackmons formats, there wouldn't be any where a glitch as such would be implemented.)
