Honestly, I wouldnt even worry about Hippowdon. It's so rare and besides, you've got tons of water moves beyond your lead to deal with it. You could even just spam hurricanes at it with tornadus, since they do a min of 59% to it. Just come in on an earthquake, rain dance, then hurricane. You do have to watch out for the stone edge or ice fang, though, but not all of them carry one of those.
As for raikou, it's fine, but then you're left without a dragon resist so you could be vulnerable if for example you're up against a salamence locked into outrage.