Considering you mean T10 encryption (LTO4 and above and STK10K) you can always do an phase 1 import of the tapes, as this information is not encrypted on the tapes.
For phase 2 import you will need to either re-create the encryption keys by using the identical passphrase, key group and key names. When bptm then see an encrypted header/image, it will retrieve the correct key from KMS based on keygroup and keyname.
A typical DR setup is a) backup PROD site KMS, restore on DR, or b) manually create all relevant keys on both sites. Encryption always adds management overhead as it is of utmost importance that you can restore. KMS data protection is very important.
I wrote a paper for a paying customer back in 2010 for NBU 6.5 cover this topic. I might consider producing something similar and more relevant for 7.1/7.5 when time permits...
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