I was unable to find a way to style the inner <ul> with a unique class or id (you can set a innerClass but will not be unique). It apperas that the innerTpl (and the outerTpl) do not have access to the full placeholders since they are considered wrappers and do not actually display any rows (thus no related document). I think the solution would be to add the unique ID to the parent of the sub:
<li class="ID19"> link text
<ul>
<li>......
</ul>
</li>
then style it by (or something like this): li.ID19 ul {style...}
Note: You can also use the [+wf.id+] placeholder to add a unique ID (not class) to each field (use together with the &rowIdPrefix to set a prefix for the id).
<li id="ID19" class="active"> link text
<ul>
<li>......
</ul>
</li>
or in other words, something like this for the rowTpl...
<li[+wf.id+][+wf.classes+]>
<a href="[+wf.link+]" title="[+wf.title+]" [+wf.attributes+]>[+wf.linktext+]</a>
[+wf.wrapper+]
</li>
Maybe someone else knows a trick that I have overlooked.
then style: li#ID19 ul {style..}