"The customer wants the RMAN recovery catalog database to be highly available so that none of the RMAN database backup jobs are impacted at the time of taking the database backups"
i think you can achieve HA for the catalog DB. (Rac and Asm should work fine)
There's no way (afaik) to use TAF with the rman backup. If you have a failure during a backup it simply fails.
There is no TAF in this situation.
Hope this helps.
You don't need active data guard for this work, just normal data guard will be fine. Active data guard is for reporting purpose, the standby database is open for read-only. The RMAN catalog is more for read-write operation.
In fact, you don't need data guard at all. If the requirement is to prevent backup job failure when catalog database is not available, then just backup without connecting to catalog. Once backup completed, connect to catalog to sync the data.