Comment 2 for bug 2012536

I've made a workaround for our environment by moving to the previously mentioned amgtar after finding this article that had some implementation examples:
https://serverfault.com/questions/915726/difference-between-amgtar-and-gnutar

It sounds like a better way moving forward now that I know about it.

These are my exact changes to amanda.conf as a diff

+ define application-tool app_amgtar {
+ plugin "amgtar"
+ }

...cut...

define dumptype server-encrypt {
    global
- program "GNUTAR"
+ program "APPLICATION"
+ application "app_amgtar"
     comment "dump with server symmetric encryption"
     compress none
+ estimate server
     encrypt server
    server_encrypt "/usr/sbin/amcrypt-ossl"
    server_decrypt_option "-d"
}

I also had to add this extra line to /etc/amanda-security.conf to allow the appropriate access
amgtar:gnutar_path=/usr/bin/tar

I haven't completed the backup to confirm its restore-ability yet but I'm no longer receiving the warnings.