The tabset component uses ice.submit and ice.singleSubmit based on the singleSubmit attribute.

I tried to test form less tabset, on page load I get the following javascript error on line 1332 in bridge.js saying 'javax.faces.ViewState' is not defined on the page:

 onLoad(window, function() {
1329 singleSubmitForm = document.createElement('form');
1330 singleSubmitForm.action = window.location.pathname;
1331 singleSubmitForm.id = 'void';
1332 viewState = document.getElementById('javax.faces.ViewState').value;
1333 });

So I had to put an empty form in the page. For testing purpose I have also added a required field inside that form(e.g.)
<h:form>
    <h:inputText required="true"/>
</h:form>
<ice:tabset>
   ......
</ice:tabset>

When I changed the tab without using singleSubmit, I could see that above form was executed and input field was validated.
When I used the singleSubmit, and changed the tab the form was not submitted and validated.