I've met the same solid resistance from some DBAs to running Oracle on NFS. It works a treat, but I appreciate sometimes it's not your choice. iSCSI's not the end of the world (not my fave admittedly) and if you force them down the NFS path and there's even a tiny hint of a performance issue, you'll never hear the end of it and it will always be blamed on NFS, even if the problem lies elsewhere. Some battles aren't worth it. Do make sure your iSCSI setup is solid however, there's plenty of performance issues to be had there too.
To answer your original question on backups, in the past I've run hotstandbys kept in sync with dataguard, then had a script take the HS out of managed recovery, snap the mountpoints/luns, return HS to managed recovery. The script also deleted old snapshots. Took almost no time and your backup is consistent. Downside is you use double the space as you have two copies of your DB, and extra overhead on the DBAs to maintain the HS. You could take this basic idea though and do something like use dataguard to run HS at your DR site and snapshot it there. Depends on your RPO and requirements for local backup.
Or, look at SnapManager for Oracle (although getting your DBAs to embrace that may be another battle in itself).