The simple answer is "yes". Perfect, flawless, and unblemished are synonyms.
The less simple answer is no. Very few words are universally interchangeable. There is almost always some connotation that is different. "Try to buy unblemished bananas" is a reasonable request.
"Try to buy perfect bananas" would be harder to carry out (depending on your standard of perfection).
An unblemished banana might taste awful.
But, in general, these three are very close in most usages.