The coal mine employee Michael speaks with over the phone is the voice of Creed.
That's genuine unscripted laughter from the cast when Rainn Wilson is reading out a list of made-up diseases. Wilson largely improvised the list, hence the amusement of his castmates.
When Michael is trying to plan a surprise event for his employees he is seen inquiring about the Coal Mine tour thinking it's a thrill ride. It's not, as the Coal Mine tour guide points out. This is a real tour at McDade Park in Scranton and at some point almost every grade school student goes there for a field trip.
The Americans with Disabilities Act (ADA) does state that existing employees must not be required to disclose medical information unless the inquiry is related to functions of the employee's job. Therefore Dwight's questioning would indeed be illegal.
This is the first appearance of Dwight's Mike Lieberthal bobble head. However, the number on the back is "7," Lieberthal was #24. This is easier to see in Office Olympics (2005) at about the 2:15 mark. Although Dwight professes to be a big Phillies fan, this bobble head isn't from Lieberthal's time in the Phillies or the Dodgers (where he played #14). It is in fact a bobble head from his time with the Scranton/Wilkes-Barre Phillies in 1994, where he indeed wore the number 7.