Why? You don’t need to be able to understand a cipher to produce plausible cipher text. You can take headers and footers from real messages and just drop in nonsense between. Or retransmit messages you recorded a few days earlier, or random mixtures of bits of real messages. The enemy still has to transcribe them, sort them out, reject the noise.

Yes. As such it would be a last resort and even then likely done very carefully (perhaps even to the point of burning a high level human intelligence source or sources as a plausible explanation for it). We're talking "no alternative" levels of desperation.