From the looks of things, you're serializing in the document/literal style, as opposed to RPC/encoded. The only thing that I can think of is that you might get some oddities from multiple references to the same object. (but you'd know the data you're sending out better than others, and you may not ever pass that sort of thing)

As for the XML Schema 2001, I think all that you need to do is to inherit from SOAP::XMLSchema2001::Serializer rather than SOAP::Serializer in your serializer. (but I've never tried doing that).