I'm working on getting Oracle 8.0.6 32bit running on Solaris 7 migrated to Solaris 10. There is no branded zone for Solaris 7 and we have decided to try to run Oracle 8.0.6 directly on Solaris 10. Basically it just works. Basically... the problem was that some of a database files are larger than 2GB and Oracle fails to recover database on these files. After checking some log files and a little bit of dtrace'ing I found out that it does a stat() syscall on each db file before recovery starts and stat() fails with EOVERFLOW. So it uses wrong API... but it seems to work fine on Solaris 7 with the same binaries. It turned out that while Oracle is starting it is calling uname() to determine an OS version and based on that information it can change its behavior (like not using proper API to access large files). The easiest way is to use dtrace to intercept uname() syscall and put a fake output just before it returns. After that everything seems to be working fine.
Below dtrace script will put "5.7" string in uname() structure for every application calling uname() with uid=300 (oracle in my case). One might also write a small interposing library and LD_PRELOAD it while starting Oracle - that should also work.
#pragma D option destructive
self->addr = arg0;
copyoutstr("5.7", self->addr+(257*2), 257);