Yes, the responses will be returned in the same order as the list of item IDs in the request. The EWS managed API sends the item IDs to the server in the order you specify - it does not change the order or spawn any threads that would mess it up.
All operations such af CopyItem, MoveItem, and DeleteItem work this way: You send a list of item IDs and a list of responses are returned without any direct reference other than the order in which they are returned.