Hi,
No, no difference basically.
The term XML over MQ just refers to the format of the payload which is in this case an XML string as opposed to a Cobol Copybook string which we often find as the MQ payload (for those customer's where mainframe is part of enterprise architecture)
Obviously, if the payload is XML then you'll probably need the XML request DPH (as opposed to the request CopyBook DPH), and there would not be a response-side DPH because the responses in the VSI would be already XML and can be put on the queue as-is (as opposed to a cobol response payload where the VSI would contain XML-representations of the copybook payload which need a response-side CopyBook DPH to transform then back into its proper data format)
Cheers,
Danny