I am exempt/salaried. Can my employer limit me to a 30 minute lunch break as long as I'm 'making up the time'? I generally put in 45-50 hours a week of actual work. Isn't my lunch time up to me as long as I'm putting in the hours required?

No, that's a myth that many exempt employees believe, but it is not supported by law. Being "exempt" does not mean you can come and go as you please. The employer has the right to mandate certain hours of exempt employees as he does nonexempt employees. If the employer wants you to take a 30-minute lunch, you do so.