I don't know if this will help you but I got seperators to work with a sitemap.  You can still customize the <hr /> tag with css if needed.

<siteMap xmlns="http://schemas.microsoft.com/AspNet/SiteMap-File-1.0" >

    <siteMapNode url="" title="" description="">

        <siteMapNode url="MenuItem1.aspx" title="Menu Item 1" description="Menu Item 1 description" />

        <siteMapNode url="MenuItem2.aspx" title="Menu Item 2" description="Menu Item 2 description" />

        <siteMapNode title="&lt;hr /&gt;" />

        <siteMapNode url="MenuItem3.aspx" title="Menu Item 3" description="Menu Item 3 description" />

        <siteMapNode url="MenuItem4.aspx" title="Menu Item 4" description="Menu Item 4 description" />

    </siteMapNode>

</siteMap>

If this is something that is going to be considered, particularly for horizontal menus, possible consideration might be given to being able to use any ASCII character to separate the adjacent links.  The ability to apply a CSS style so that the characters could be hidden would also be advantageous.

Such a thing would satisfy the W3C Accessibility Guideline 1.0, Priority 3, 9.5 -- "Separate adjacent links with more than white-space."  Border attribute via style sheet is not enough to satisfy this requirement. A few designers might appreciate the ability, for example, to add a horizontal bar between menu items.

Disregard the above.  The Priority 3, Section 9.5 of the Guidelines are met and do not need an ASCII character between the links.  The horizontal menu is rendered inline by the style sheet.  Since a Braille reader doesn't interpret style sheets, the menu links are separated by a line return, bullet, whatnot, by virtue of the unordered list definition. Apologies for any confusion.

Thanks for the sitemap node title suggestion of &lt;hr /&gt; for a horizontal rule separator.   An additional alternative for those who want to add a style to an ASCII character to the specific separator would be:   <siteMapNode title="&lt;span class='Specific_Class_Name'&gt;|&lt;/span&gt;"/>  You can define the class of the span to format the ASCII, in this case a vertical bar, character.  Sort of down and dirty but it works and validates.  Just keep in mind that when style sheets are disabled, the separator will render as a list item.