Stockpile Hippowdon just seems pointless, imo. Hippowdon is great for stall, but without Stealth Rock it doesn't bring anything to the table. Swampert is better for any other style of play, imo. Obviously both have access to Stealth Rock, but Swampert has a decent special attack stat and a better typing for pairing up with stuff like Shaymin or Heatran. Stockpile Hippowdon loses miserably to Gliscor (Taunt + Toxic), Skarmory (faster Whirlwind), and Gyarados (Taunt, Roar, or Dragon Tail), and Dragonite (Dragon Tail). Not to mention it doesn't do much damage and can't set up on much (still loses to Toxic, anyway).
I don't know, how about sandstorm? :/
Swampert has no reliable recovery and has less defense. Stall as a whole loses to Gliscor. Swampert can't beat Taunt Gyara and Skarm without a lot of freezehax. Dragonite will never (rarely?) run dragon tail, with negative priority, low bp, etc.
Also, Hippowdon's Earthquake has four more attack points behind it.





