Yep you can access it by finding out the datatype's id - by hovering over the datatype in the tree and checking the url displayed in the status bar at the footer of the browser.

It should read something like

javascript:openDataType(1023)

Then take that id and you can use it as follows in an xslt macro

<xsl:for-each select="umbraco.library:GetPreValues(1023)//preValue">
    <xsl:value-of select="." /><br/>
</xsl:for-each>

The xml you transform will be something like this

<preValues>
   <preValue id="10">PHP</preValue>
   <preValue id="11">Joomla</preValue>
   <preValue id="12">SQL Syntax</preValue>
</preValues>