@cwebber I have seen symmetric ciphers with random, ephemeral keys used for producing pseudorandomness for wiping drives (and have done so myself)...perhaps this is just a lazy/familiar way of doing the same thing from the perspective of whoever authored that? openssl is often used instead.

dd with /dev/urandom is most often avoided not because it's a bad idea, but because it's relatively slow compared to e.g. using openssl for the aforementioned purpose.