Yes you can look for "XML API Programmer Guide for VNX for File 8.1" in support.emc.com and I don't see XML API for VNX block ....!!
I've found XML API for VNX File (EMC® VNX™ for File XML API ). It is for version 7.1 only.   Some questions: - Does VNX for File 8.1 (VNX II) support this XML API? - Is there XML API for VNX Block ?
VNX XML API