No health insurance will cover anything for anyone who entered the scheme not disclosing a past treatment for cancer. Health insurance concerns do not go away (quite the opposite) by not disclosing cancer.
Disclose it when they ask for past medical history, then, not at a job interview. At that point, they've already hired you, and this becomes an annoying health insurance hassle and not a reason to not hire you. Why stack the deck against yourself?
You have to disclose it at some point, but it might be more prudent to disclose it as part of the health-insurance registration process after being hired.
Yes, but disclosing it in the resume/CV is way to early. You are basically asking potential employers to pass on you before you have a chance to show how valuable you are.