Is there any association between children who are "late talkers" and children who become selectively mute later in life?

Not That I am Aware. Speech delay is related to immaturity of expressive language development and the part of the brain that controls that function. Mutism behavior is unrelated as far as i know.
Probably not. Selective mutism is a subset of anxiety disorder. Late talking can be caused by many things, including hearing loss, adhd, learning disabilities, language processing deficiencies, apraxia, cp. Check with your pediatrician for assessment and possible referral to early intervention with speech/language professional.