It's been several months since I worked with Weblogic (6.1) but I don't remember it behaving as your example shows.
Your root directory is SimShop so everything should be relative to that ....
<%@ include file="wwwroot/includes_jsp/ADMIN/sniffer.shtml" %>
Should work the same way with Tomcat.
That's assuming, of course, that you've got a top level directory in your war named wwwroot.
BTW, you really should use