The problem is that for a content management system that supports multiple sites and supports different skins on different pages, it is difficult to design with tools like that. It can open a solution just like Visual Studio can but in both cases there is a distinction between runtime and design time. These tools are great if there is no difference in how things work at runtime than at design time (ie if you are editing standard html files there is no difference in how they work at runtime vs design time), but in mojoPortal things are quite different at runtime because we load the css and skin files from the site specific and often page specific skin folder based on data from site setting and page settings stored in the database and design time has no context for that.
So the short answer is no that tool will not help you much in designing for mojoPortal, it is best to work directly with the skin files and the web browser for viewing the results of your changes. You could use such tools for editing the CSS but it won't add much value vs other text editors other than maybe a little CSS syntax highlighting.
The best visual design tool that one can use with mojoPortal is Artisteer. But then you export the html and do a few steps to make a mojoportal skin from the html.
Best,
Joe