Yes, it is possible to install oracle 8i and OAS on the same system. But the trick is that if first install the 8i and then the OAS. If you were to do vice-versa, the OAS would start missing the libraries under its link.
If you are planning to go for OAS, I would suggest that you start with the iAS (Internet Application Server) as support for OAS would soon be unavailable. Since iAS comes with an apache module, it would be a great point to work your way out through fiddling with it.
There is the catch. At this time you have to reinstall your reports server. I had the issue of OAS not getting initialized, after I did an OEM 2.2 install. So I have to revert back to my OAS on the test. I haven't fully started to play with this. One of the other things is that matters I beleive is that where you put the java components.
Here are some of the differnt ways that you could avoid this problem.
1 Forget the OFA, and have different homes for these installs.
I Installed Reports 6i in the default_home (c:\orant) and then installed oracle 8.1.7 in a different home ora81home (c:\oracle\ora81).
Infact 8i did not even finish its installation. It did not create the starter database, did not install the database configuration assistant and a lot of other stuff. Infact it des not even show the 8i installation in the installed product list in the oracle installer.
If I install 8i first and then install reports 6i it installs fine. ofcourse they have to be on different Homes as oracle does not even allow you to install reports 6i in an existing oracle 8i home.
Any reason why installing oracle's products is so cumbersome ?