Hello Davensac,
If other apps are making the same calls as the PCDr products then yes the return values should be the same. Please keep in mind, that other apps may have the same test name, but they can be using different values that those used in PCDr products, which would result in different results.
On the same note, if a HDD manufacturer has an app to test SMART, such as Western Digital or Seagate, then their results could differ from PCDrs as they have access to proprietary threshold values. If these HDD manufacturers have shared these values with us or with other SMART apps, then those values would match.
I hope this helps.