It's in Sinnoh, is it not? Also Kanto, but only in GSC/HG/SS.
Roselia, Chimecho, and Meditite may technically exist in Hoenn, but all three are a lot more common in Sinnoh. I consider it quite telling that they all appear (well, Budew and Chingling, not Roselia and Chimecho, but you know what I mean) when you play the Sinnoh Sound, not the Hoenn Sound, in HG/SS.
Creator of Jay's Journey (see quote!) "It's not ten years old! Therefore, it sucks!" - Nostalgia whores everywhere