As you can see in my example - the content of the first row in wrapped in a div with the CSS class I gave my ace:column instead of just set it to the TD - like it does for the others. I think thats an issue that should be fixed.

XHTML:
<ace:dataTable value="#{bean.items}"
var="item"
styleClass="table">

  <ace:column styleClass="first">
    <f:facet name="header">
      Header Text
    </f:facet>
    #{item.something}
</ace:dataTable>

HTML Output:
<div class="... table" ...>
<table>
<thead>
<tr>
<th class="ui-widget-header first">Header Text</th>
</tr>
</thead>
<tbody>
<tr class="ui-datatable-even">
<td>
<div class="first">First Row Something</div>
</td>
</tr>
<tr class="ui-datatable-odd">
<td class="first">Second Row Something</td>
</tr>
<tr class="ui-datatable-even">
<td class="first">Third Row Something</td>
</tr>
</tbody>
</table>
</div>