Assuming biological compatibility, it would likely be more effort than it is worth to consume humans on a large scale. Any alien with interstellar travel would be in a far better position to eat the meat that we do. Cows, pigs, goats, sheep, etc are far more docile and easy to maintain and slaughter large populations of. Though if humans taste good, being a delicacy is not out of the question.
I also have doubts about such an advanced species using extensive slave labour. Simply because their technology would povide much greater efficiency using a few of well educated and motivated individuals than masses of slaves doing manual labour. Of course, being exploited without actual slavery is another option.