Does Utilitarian or Kantian Morality Approve :
1) Capital Punishment
2) Use of torture in interrogation of known terrorists
Neither approve or deny capital punishment and torture. They just provide a framework for evaluating how ethical these are depending on the context.
The Categorical Imperative is supposed to provide a way for us to evaluate moral actions and to make moral judgments. It is not a command to perform specific actions -- it does not say, "follow the 10 commandments", or "respect your elders". It is essentially "empty" -- it is simply formal procedure by which to evaluate any action about which might be morally relevant.
Kant disapproves of both. In both cases you are using the victim as a mere means. For Kant, the ends do not matter if the process does not respect autonomy. Punishment, therefore needs to improve or reform the person punished in a way of which he would be completely certain to approve either before or after it takes place. Killing him does not address the problem, it just ends it. And torturing him to make him betray his principles is a change he would be unlikely to see as an improvement.
Utilitarianism has no absolute opinion on either. It would depend upon the value of safety and the fear of tyranny in your specific society, as well as more subtle things. If torture is OK, it may be used by the unscrupulous in questionable situations that encourage over-controlling the population. After all, who is and who is not a terrorist is subjective. And since it really is not a good source of intelligence, this may outweigh its value.