I believe you have to have your project point to the jar files for J2ME Polish, now you will be able to access their classes. In the Project Settings there is a part for "Paths" in that screen there is a tab for "libraries/classpath". CLick the Add Jar/Classpath button, then select the jar files that you want to add to your classpath, and voila.
1. The tags are in a jar or a DTD, and putting that in the classpath works. 2. There is also a place to add tags that are valid, but you type them in yourself. So if there are lots of tags, then you type a lot into the settings area.
I am going to start up IntelliJ to see if I can find that setting. I don't recall exactly where it is. And it might just be for javadoc tags, like those you use in XDoclet.