I can't speak for other companies, but in my 3 years with PAM I've yet to hear of a driver making it to orientation and being sent home due to falsifying their application. I'm not saying it hasn't happened, I just haven't witnessed it. Plus, this is in the PAM section so we can only speak for PAM. Also, the majority of students don't go through orientation until they're off a trainer's truck. Some heads would be rolling if a guy got on a truck and later info came up he's disqualified.
I'm going through hoops and hurdles due to a shoulder injury I had earlier this spring. I am fine, pain free, don't need surgery, and wasn't even work restricted for/at my previous job, but PAM has me on hold until they get my records from the orthopedic doctor stating that it won't be a problem. It's frustrating, but at least they are thorough.
The OP asked the question "do companies do complete background checks before orientation" Notice the word "companys" Now had the question been about PAM I would not have posted.