ora8.so is aolserver Oracle driver. I you may forgotten to compile it. On the unpacked aolserver 3.3.1ad13 its included there. Just go the directory and compile it and install it on the aolserver bin directory.
There is also an oracle driver on aolserver sourceforge page, not sure if this one is better. Its been a while since I installed Oracle for OpenACS.
Maybe others with more recent experience with Oracle will be able to comment more.