If data was acquired unethically and made free to use, would it be unethical to use this data? A specific example might be the 'medical experiments' performed on the Jews by the Nazis.
"Ethical" is a very subjective subject, most of the time*. But in general, I would say it's unethical not to use the best information available when treating someone (talking medical ethics here, as per your example) regardless of how that information was gained.
If the first experiment with cyanide was to poison someone with it, and only then realize that it's lethal, should everyone else ignore that information and continue to give it to patients?
Of course, there's a fine line between "using information gathered unethically" and "indirectly funding/encouraging the unethical gathering of information". It's important not to cross that line.
- unless you're dealing with a specific, formal set of written ethics, in which case this answer is "that depends on what your chosen body of ethics says".