All the APP 9 customers should use oracle 12.1 clients for their configurations 

App10 Customers on or under UPD6 need to use 12.1 clients.

Therefore in general oracle client, 12.2 is not supported by any IFS installations which are on or below APP10 UPD6

From UPD7 onwards the DP is compatible with the oracle 12.2 clients.

The below table elaborates an overview.

IFS supported platforms documentation for APP9 and below APP10 UPD7 customers