Nope, with that kind of spread you won't get HP Grass, only Electric (odd number in speed) or Water (even number in speed). You are still right about the base power. The optimal spread for your purpose is 31/xx/31/30/31/01 with Atk being an even number (0,2,4, ..., 30). Alternately: In the case you was lazy with breeding, a faster way would be xx/30/31/30/31/01. HP is not critical for HP Grass, but because HP is such an important stat for Politoed we would recommend you to go the first route.