The construct you are using is for standard JavaBeans. Enterprise JavaBeans require a bit more work to discover them and use them and the jsp:useBean directive is unable to achieve this directly, using the EJB exposed interfaces.
You can write a JavaBean as a proxy to the EJB if you are really set on using jsp:useBean.
that was just the nudge i needed. Changed to use a bean proxy, and it's all good!