Is it possible to pass a nuclear imaging stress test and the EKG to show you had a mild heart attack in the past?

Yes. An old heart attack might not show up on the stress test if it was very small. However, some people have and ECG that looks like and old heart attack, but wasn't. This artifact commonly occurs in women. Talk to your doctor to see which is most likely.
Yes. Yes it is possible if subendocardial or nonstemi. (non st elevation myocardial infarction).