Hmmm, this one will always need some clarification first.
XmlSchema = types defined in xsd
CLS = common language specification
isomorphic = basically you can map 1-1 from one to each other, it is a mathematicall concept.
My anwser is that they are in a sense, that is what partly we do when mapping from OO to SQL via a middle layer of mapping to XML like in Hibernate or .NET entities framework. We can map String class to xsd:string type, int to xsd:int, etc...