Yes,
Struts 2 provides AJAX tags that use Dojo under the covers. However, there is nothing stopping you from using any other Javascript framework - just don't use the Struts 2 AJAX tags. In fact, Struts 2 users have developed plugins to provide extra integration with other Javascript libraries such as the YUI plugin:
http://cwiki.apache.org/S2PLUGINS/yui-plugin.html