We don't use safety relays at all anymore. We use CR30 for everything, the diagnostic feedback can take a long troubleshooting time to zero with those few LED on the face of the unit.
As Ken has stated OSSD are for switching. Whe they fail statistically they will fail in the safe conditions. When you use EDM (External Device Monitoring) in conjuction with a 700-HPS2Z24 as arpus4KM stated you can monitor that the unit is switching to the correct function. Ie when I say switch off, the relay sill feedback a signal and say I switched off.
Think of this as a "Configurable safety relay". The safety inout goes to this unit not the PLC. This unit handles all the logic for the safety then it can be a signal to the PLC.
I try to explain it as input , logic , output. Just like a PLC. In safety my goal is to keep people then machine safe. By historical design with tried methods removing the hazard is (safestish with some exceptions). If you take all the inputs to the PLC and rely on the PLC to pass the data to the safety circuit you have just introduced another point of failure in to the safety chain. Lets reduce these to the needed minimum.
Sorry Im rambling I've been up since 5am yesterday and am having a liver biopsy today. Im a little excited somy thoughts are all over the place.