We are in the process of upgrading the database from 10.2.0.2 to 220.127.116.11 database. Currently Client is using pro*c(from 10.2.0.1 client) on different machine connecting to 10.2.0.2(Will be upgraded to 18.104.22.168) database. I gone through certification matrix and found that 22.214.171.124 is supporting till 10.2.0.4 clients. My advise to CLIENT is that CLIENT has to install the latest possible certified client and need to re-compile all their pro*c programs in the new client. Please correct me if there is any correct required for my understanding.
It should generally work as expected - see the FAQ section here - Introduction
It would be best to test the application and all related functionality by performing a test upgrade - only then would any issues surface