Mobs don't treat sculk shriekers as obstacles. Note that they do treat sculk sensors and calibrated sculk sensors, which have the same collision, as obstacles.
Steps to reproduce
Set up a row of shriekers with a ceiling 2 blocks above
Spawn hostile mobs on the other side
Go in survival mode (x)The mobs are unable to reach you
In 1.20.2 Pre-Release 3