The purpose of importing the HTML, JavaScript, CSS would be to represent these pages of our application in Sequence Diagrams for given business processes. I did try the route of importing JSP, etc with the source code import option in EA, but it did not work, it filters on the extension of the file "*.java" so it doesn't import .jsp, .css or .js files. We did use this import option on our Java files, worked great.
For you and others seeing this post, only solution we found was creating a "Web Modeling View" within EA, then opening the diagram, then copying each JSP page "via copy\paste" onto the EA diagram. You have to copy one at a time in this process. After pasting, when prompted with the EA modal, select the option to put file in as "Artifact (Internal)".