EDIT: If I understand your comment correctly, you have an existing Oracle Spatial instance. And you have (or will have) an existing ArcGIS Server install. And you want ArcGIS Server to view the data in Oracle without having to install ArcSDE (and its associated database objects) on your Oracle instance.
Yeah, I think you could get the data OUT of Oracle. That would go like this:
- You'd have to set up Oracle client on your ArcGIS Server machine(s). See here.
- You'd have to set up Oracle client on your ArcGIS Desktop machines.
- You'd have to register your Oracle instance with ArcGIS Server so that any feature services you deploy will get their data direct from Oracle (rather than having their data copied upon deployment). See here.
After that you could make ArcGIS Server map and feature services that view the data.
Those services would probably not be editable through ArcGIS, though. Geodatabase editing in ArcGIS seems to need those extra ArcSDE metadata tables. (But I'm not an expert on that corner of the ArcGIS software, so maybe someone else would say different.)