I have an ear project which has 3 other other projects in its deployment assembly. One is a web project, one is an ejb project and the last is a utility project which contains only interfaces. (see below for org.eclipse.wst.common.component)
I can add this to a jboss 6.x server. If you unfold the application in the server view it seems like it knows the jar is supposed to be there. It is missing however if you actually look in the deployed ear.
According to a colleague of mine (on another continent) it works for him. I can't get it to work for love or money.