must one call Calling super.jsonSerialize(...) or is this done by SeroUtils.jar in the same way as for writeObject(...)?
call super (as seen in the code...).
What is the JsonReader in jsonDeserialize(...) for?
Yes, you must explicitly call super for the serialization to work properly.
The JsonReader provide access to some useful utilities that you may or may not need. Some code needs it, so it's there.