Would it be unhealthy to have slightly blurry vision wearing contact lenses?

Usually not : Contact lenses when properly fitted and of the right power should give you clear vision at the distance for which they are supposed to correct. If your blur is right away with a new prescription, then it should be re-evaluated by the ophthalmologist who prescribed them. If the blur is an acquired thing over time. Then your eye power may have gradually changed and a new lens needed.