Counter anecdote, I was an exempt salaried engineer at General Dynamics, and got paid time and a half for every hour over 40, if I worked more than 45 hours per week.
It boosted my annual salary noticeably, because we worked 45-50 hours nearly every week. I hear that the OT policy still exists, but few people still get OT because of the DoD sequester. But in 2010-2012, it was very nice.
That's completely up to the discretion of your employer. The reason for classifying an employee as an exempt employee is to exempt them from the Fair Labor Standards Act, usually with the goal of excluding them from demanding overtime pay. I'm not sure what the benefits are for classifying someone as exempt but then still giving them overtime pay.
It boosted my annual salary noticeably, because we worked 45-50 hours nearly every week. I hear that the OT policy still exists, but few people still get OT because of the DoD sequester. But in 2010-2012, it was very nice.