Can an ODB2 reader detect errors even if there is no check engine light present on the dash?

Many can show pending codes. Pending codes are codes where an improper event has occurred, but not enough to warrant turning on the check-engine light.

Beyond that, to see activity that has not been identified as a problem but might be leading that way, you'll want to look for a scanner. You could use a scanner to see the current activity and compare to known measurements and experience.