Is it at all possible to use Oracle.ManagedDataAccess with Oracle DB v.8.1.7? I've searched for hours, but failed to find a definitive answer anywhere.
No. ODP.NET Managed Driver only supports databases back to 10.2. As it is a relatively new product, there aren't old versions to fall back on.
The problem is the networking protocol changes over time and Oracle promises backward compatibility for two major versions.
If you must use ODP.NET and Oracle Database 8.1.7, consider using ODP.NET Unmanaged driver version 10.2. It is still available here: http://www.oracle.com/technetwork/topics/dotnet/utilsoft-086879.html Of course, using a very old version of ODP.NET introduces it's own limitations, such as lack of Entity Framework support and other things.