Hi Joe,
Your solution is correct you have to override what the Artisteer CSS is doing. It isn't that the jqueryui is using the artisteer styles its just that the artisteer css selectors are broad enough that they also impact the same elements that jqueryui is trying to style and their rules win because the jquery ui css is above it and rules lower within the total css have more precedence.
For the same reason of precedence your fixes are/should be lower in the css than the main artisteer css in order to override them.
Actually Artisteer also has some clashes with jQueryUI Slider both in javascript they include and in css. In fact when I implemented the skin exporter for mojoPortal I have to do some find and replace to rename some things in their javascript to make them unique because they were breaking jqueryui slider functionality. The Artisteer slider is just an image rotator thingy not anything remotely similar to what jQuery UI Slider is.
Hope that helps,
Joe