Is "indifferent of" correct in this sentence? Is it ever correct? Should I replace "of" with something?
"In regards to hacking, do you approve, disapprove, or are you indifferent of the practice?"
It is correct, but you should add to, toward, or towards before it. Also, you should replace regards with regard. While it's not technically incorrect (according to some; there is debate), it sounds more professional.
So the sentence should be:
"In regard to hacking, do you approve, disapprove, or are you indifferent to the practice?"