Do violations of basic ethical principles in research invalidate the results of a study?

This question cannot be simply answered with "yes" or "no", as there is no absolute, mechanical correspondence between violating basic ethical principles and the validity of research results. Strictly speaking, the scientific validity of research results - whether the data truly reflects the state of the research subject - and the ethical compliance of the research belong to two different dimensions: even if a study has serious ethical flaws, the data obtained may still be "accurate" at a purely empirical level. However, in the academic practice of contemporary population research, ethical violations almost inevitably lead to research results being considered "invalid" or "unacceptable" within the academic community.

This depends on what you mean by basic ethical principles. If you refer to scientific integrity (honesty and transparency) in reporting results, data fabrication of falsification, cherry picking, p-hacking .. these are definitely practices that should invalidate the results of a study. However, if you are talking about ethical principles related to the gathering and use of personal and sensitive data (as defined for example by GDPR), such as violation of privacy and not considering respect for communities, these do not invalidate the results but it is failure in considering ethical and legal issues in the study and if the results are to be published this is problem! 

Ideally, yes— but unfortunately, "basic ethical principles" doesn't invoke any particular codification. If you can reference a relevant professional society's established ethical code, then yes, that's what it's for, at least insofar as a given author identifies as a member of that society.