Chef

That area was where you'd normally go to get Shaymin in D/P/Pt if you had the Oak's Letter from Wi-Fi gifts. It would connect to Seabreak Path(probably what that bit you see in the image is), a very long strip of land covered in flowers connecting to a small island at the top right corner of the sinnoh map, with the island being Flower Paradise where Shaymin would be. Of course in MMO it's different, we have the shaymin pillar instead at various locations once you have 12 dead flowers. We don't have Oak's Letter here, so you really shouldn't see that at all, so it's a small visual glitch.

It has HA on gym leader rematch teams, but the dragon part is true, probably won't be paired with gyarados, but if it was paired with it for raid, would make it a tough fight to only have rock weakness to exploit.

A part of me is hoping it sets up the rain turn one and it's permanent like sand was in Excadrill fight, and that it uses Dragon Dance at the start, with the ability being Moxie on it. Just pair it will HA Seaking (Lightning Rod) and it would be a fittingly tough final fight before Shaymin!

For Sinnoh Raid Dens I've found on Routes: 207, 210, 212, 214, 217, 221, 222, 225, Eterna Forest, Fuego Ironworks, Iron Island, and Ravaged Path. Will need Cut for 212, Surf for 221, Rock limb for 210, Surf for Fuego Ironworks, Rock Smash and Surf for Ravaged Path, and Surf for 225. 217 has Lopunny. 222 has Purugly. 225 has Grumpig.

For that lone item? No, it's a rare candy if I recall correctly. But if you want an easier time getting Hippopotas from the Ruin Maniac Tunnel, definitely worth doing, it will also open up a room with just unowns "?" and "!" if you ever want to shiny hunt those.

They do, the Johto Beasts have Inner Focus as HA on all three which I feel is fine if they ever wanted to add that. But then there's Zapdos and Moltres, who's HA is Static(Lightning Rod Gen 5) and Flame Body respectively, which might be too nice, especially for Zapdos.

It will be. https://forums.pokemmo.com/index.php?/profile/9-kyu/&status=26285&type=status