"Glom" is just American slang for "stick together", not a technical term.

You're right that "glomming" is a special case of a mixture of distributions. But I suspect that the rather simple formula for the entropy of a probability distribution formed by 'glomming' gets more complicated for mixtures of probability distributions that don't have disjoint supports.

Yes, that formula for the variance of a mixture is somehow related! I'm not sure exactly how to fit them in a common framework....