I doubt that reversion from an intercooler would yield air cool enough to cause thermal shock to the compressor side of a turbo. If you found some bizarre way to route fresh air into the turbine, maybe. I'd say the BOV is there to prevent overpressure which leads to detonation, which leads to broken motors. While it's true that backpressure might stall the compressor, I'd call that a secondary purpose.

 

The wastegate actually prevents over boosting(or overpressure) if you prefer. Since the wastegate diverts exhaust gases from the turbine to hold boost at a constant pressure. Also the primary purpose of the BOV is to prevent a pressure backflow and stalling of the turbo. Since stalling or reversing the compressor turbine is gonna do the same to the exhaust side....

 

:doh: I was thinking wastegate, my bad.