1)In RAC all instances will show same data from asmcmd. To use asmcmd, you need to export ORACLE_SID to +ASM4 by logging on 4th instance.
2)When you create database using DBCA, oracle automatically add’s database to the OCR. In case you wish to add instance, then use DBCA instance management option to add instance which will also register the database. In case you created db/added instance manually, then you need to use srvctl command for same