Based on the Q & A only XYZ, Synchro, and fusion monsters summoned from the extradeck goes to the EMZ. Extradeck monsters that are summon from the grave or banish zone (after being summoned from the extra) will go to the normal monster zone.
Please don't make assumptions about the Extra Monster Zone. The current mechanics have no restriction on which Zone you can place Omega in when it returns to the field. This may or may not change with the new rules.
What we currently have states only that Extra Monsters can be Summoned from the Extra Deck only to an Extra Monster Zone or to a Link Monster's Linked Zone. Summoning from other locations doesn't have this restriction.
Remember that the key word is summon, since omega was in a specific zone when it left, its not summoned again. As was mentioned, we need confirmation on this, however for now it can be assumed it can't return if something else occupies that zone