Yes, that is how I tested it, but there's nothing magic about DNS either. Remember that this depends on the site owner and the users cooperating to put misleading data into the SNI, while still functioning properly. It isn't often useful, but it is sometimes convenient.

Basically, whatever the client does that results in a successful map of name to address (including the textual representation of the address, to the address) will cause the name to be sent in SNI, and will be used to select a matching cert on the server side.

If you do use DNS, your lookup might have a suffix appended automatically, depending on local nameserver config.