Oracle AS has all sorts of default files, scripts, Data Access Descriptors (DADs), and other features that people forget to turn off when deploying these servers. In some cases, they can provide valuable information about the server or even be useful attack vectors for more serious vulnerabilities like SQL injection and file disclosure.
In the past I've always had to manually crawl through these servers, and would perform manual tests based on guidance from two excellent whitepapers:
- OWASP's "Testing for Oracle"
- NGS Software's "Hackproofing Oracle Application Server"
OAPScan will automate a lot of those testing steps for me, albeit as noisily as any other tool that crawls/scans web servers. If nothing else, it's scan database can be a good reference if you want to learn about what things to manually check for, in concert with the whitepapers I mentioned above.