1) You can configure docker's daemon.json file on Kubernetes in the same way as every other system running Docker (in fact, you can apply it with a daemonset if you want to).
2) Yes, every other image mandates where you should get it from - Docker Hub's are unique in that regard.
Normally the registry the image is pulled from is configurable in the Helm chart.
1. it requires a change on the docker daemon config. On many container environments like k8s it's hard to manipulate that setting.
2. it works only for the default "implicit" index registry, aka docker hub. Not all images are distributed from that place.