I don't remember having any JSP include issues since WAS v5.1 days.... but you mentioned that your app. works OK on stand alone WAS v5.1... which is good
but
...you cited that same doesn't work on RAD. First of all which version of RAD? And most importantly which version of in-built WAS
test server that you have in your RAD? If your WAS test server "VERSION" in RAD doesn't match with your standalone WAS v5.1 ...then bring up your WAS test server version in RAD to the same level of stand alone server (i.e. v5.1 per you) and see if that makes any difference.
Cheers,
H. Kanthi