Yes, some lifters do grind their teeth from clenching while lifting. The overall tooth wear from grinding depends on how severe your case is. Everyone is different. He would be able to tell how much this can affect you by noting the wear on your teeth already. Many people grind their teeth at night without even knowing. Often this can be attributed to stress as many medical, dental and vet school students end up grinding their teeth over the years of schooling.
Many of the bacteria found orally can end up in the plaques that occlude blood vessels. Also, oral health is often directly related to overall digestive health as you get older. People are keeping their original teeth longer whereas 50 years ago, 30 year olds were often being fitted with dentures on a regular basis.