Depende das versões exatas:
-
Usando o 11g Client com 10g Database diz
"Metalink 207303.1 is the client/server interoperability matrix. If by 11g you mean 11.2 and by 10g you mean 10.1, the 11.2 client will not work with a 10.1 database. If the client is 11.2 and the database is 10.2, it should be at least 10.2.0.2. If the client is 11.1, the database should be 10.1.0.5 or 10.2.0.2 or higher."
- Está ok para usar cliente oracle 11g com um servidor 10g? concorda com isso (com menos detalhes)