In Arathi Highlands, Zidormi is down at the south end of the zone by the bridge to the Wetlands. There’s no alternate version of the Wetlands, so you won’t find Zidormi in that zone.
As for the exploration achievement, in Arathi don’t forget to follow the path around Stromgarde Keep to Faldir’s Cove. There’s also several caves on the eastern side that you might need to enter - Drywhisker Gorge, Witherbark Caverns, and Boulderfist Hall.
In the Wetlands, don’t forget to go into the stone quarry with the animated raptor skeletons (Whelgar’s Excavation), the Angerfist Orc area just east of there, and the spider-filled cave near the tunnel to Loch Modan. And if you go through the tunnels to Loch Modan, partway through there’s a small area with some orcs in it that might be considered part of the Wetlands, so you should go there. You might also need to swim down Menethil Bay to the area across from Menethil Harbor where there are some Murlocs.