Good summaritan covers more than diving injuries...I do not know if anyone has ever been sued in a diving related o2 administration, however, in Michigan Good Samaritan Law only applies to CPR and Basic First Aid. Oxygen administration is considered a Licensed or Prescription requirement which no longer covers it under good Summaritan. Like I said I dont know Dan's O2 class and what it would/would not cover however, here in Michigan O2 delivery is not covered under good samaritan, Dan might have their own coverage for people who took the course. Are you going to be sued? who knows! is there a chance you could be sued and not covered by good summaritan in Michigan....Yes.
(Just looked up the statute, it covers Basic First Aid, CPR and AED usage in Michigan..It also does not cover any one who has a duty to act..ex on duty Police Fire Ems...etc)..please look up your own States Good Samaritan Laws to know what is covered.