All my dogs are microchipped. I’m not aware of any obligation for vets to report microchips. However if a pet is lost a scan can detect the microchip. Animal shelters scan for microchips routinely.
I recently found a cat which was microchipped. The first vet scan did not detect it. Another vets scan did. I’m sorry I found the owners because they were complete dummies. The cat was lost again because they couldn’ t be bothered to transport it safely.
I was so frustrated with our local shelter. Our dog ran away many years ago (was chipped and the chip was registered). He was brought to the shelter by some Good Samaritan, but they didn’t scan and we were told no dog fit the description. We ended up physically going there anyway and there he was. They then charged us for room and board as well as shots (he was up to date and still wearing a rabies tag with our vets number). All in all it cost us a few hundred to get him back!