以下のスクリプトを試してください。問題が発生した場合はお知らせください。
import javax.xml.XMLConstants
import javax.xml.transform.stream.StreamSource
import javax.xml.validation.SchemaFactory
//Load the XSD from a file
def xsd = new File('/C:/schemaFile.xsd').text
//Get the XML from the response
def xmlHolder = new com.eviware.soapui.support.XmlHolder( messageExchange.requestContentAsXml )
def xml = xmlHolder['//result']
def factory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI)
def schema = factory.newSchema(new StreamSource(new StringReader(xsd)))
def validator = schema.newValidator()
try {
validator.validate(new StreamSource(new StringReader(xml)))
} catch( e ) {
assert false
}