RoboHelp works with files in XHTML format or HTML format. So yes, I'm thinking you will need to change them in some way so the result is XHMTL or HTML files before RoboHelp will understand and use them.
(I have no clue what an XSLT transformation is, is that like time travel?)
@Rick: XSLT is a transformation language to tranform an XML document into another text based file such as XML or HTML.
A RoboHelp Project is a collection of XML and HTML files to make a coherent whole. I don’t know what a SUManual is, but there are several ways to go to make it into context sensitive help.
1. Directly generate a CSH help from the XML source, but this will required creating a skeleton system for context sensitivity, table of contents, etc.
2. Roundtripping to RoboHelp:
a. Using a script/application to set the barebones project.
b. Using XSLT to transform your XML into topics.
c. Using XSLT/script/application to create the Table of Contents, Index and Context Sensitive data.
d. Using a script to create the help system and publish it to the location you require.
Such a system will require some work to set up. But when it is set up, you should be able to convert your XML documents into a help system in minutes.