Is the correlation between different members on a person's body directly proportional? For instance, can a person with giant feet have small hands?
Yes, within normal variations of individuals.
It may be possible for a person to have an extreme appendage size compared to other parts, but that would be an abnormality. The following site describes a statistical test done on body proportions.
This site is more about the normal range of variations that are considered normal. None of them is an extreme case.