UITest framework supports Sharepoint 2007 & 2010 as any other ASP.Net application. This blog gives you an overview of what is not supported in SharePoint in Visual Studio 2010 release.
Since UITest uses IE pluggin for SharePoint also (as both uses IEDOM), please read the two deep dive blogs that was published on IE plugin to know about how this plugin works and how to troubleshoot failures.
UITest framework – IE Plugin - Part 1
UITest framework – IE Plugin - Part 2
UITest supports SharePoint applications hosted on both IE7 and IE8. FireFox is not supported as SharePoint has different functionality between IE and FireFox.
UITest Support Level
Author – Venkatesh Sargunesan
Test Lead - CodedUITest