In my previous post http://achatzia.blogspot.com/2007/09/stand-alone-oracle-http-server-vs-as.html I said that there are two separate code trees for the OHS.
Now I found at least one difference. If you have a look at the mod_oc4j.conf file you will see that the standalone version includes
LoadModule oc4j_module modules/mod_oc4j.so
while the AS version does include
LoadModule oc4j_module modules/ApacheModuleOc4j.dll
This of course is the Windows version. If somebody wants to check if such a difference exists with a Unix version I would like to hear that as well.