Based on the pictures on that site there is indeed no water in that area.
Having an admin post here to confirm this is a mistake in the pokedex or not would be appreciated.
As for alomomola being a pheno only poke I think is fine.It requires teamwork and some time to find it.Its like the feebas tile.There is ALOT of tiles in route 119 hoenn.
One time when a tile was found I had to use superrod and find 10 wild pokes before I found feebas.A fact very scary for when you need to find the tile in the first place.
Besides most people want them for the OT pokedex and its nice to have some rare pokes.
As for me I was patient and waited for people to share pheno with those poke to complete my OT pokedex.