There are lots of examples in which artists that Stalin respected where crushed less hard than one might expect them to be crushed, Zamyatin comes to mind.
Evgeny Zamyatin was not a singer, so I really dont think this proves singers were uniquely safe. Also, reading story, he had contacts which allowed him to get passport and leave as he was persecuted.
The political persecution he was under was not that unusual for times. It strikes me more like "I heard many stories kinda like that" then super unusual.
http://soviethistory.msu.edu/1929-2/proletarian-writers/prol...