You don't give enough details (which Oracle?, what type of replication?) to give a complete
answer, but I do know that you can't run an ArcSDE service in an instance which is replicated
by a logical Data Guard configuration. Generally speaking, advanced database configuration
and ArcSDE application servers are incompatible -- Using Direct Connect connections will
always be your best solution when RAC is involved.
There's little reason to use multiple logins on Unix hosts -- they are not subject to the same
limitations found in Windows servers. I regularly run three to five instances of different
versions of ArcSDE on Linux boxes with a single UID. The only difficult part is setting up
'.profile' configurations for each instance and being sure to run the right one before
starting each service.
- V