hi,
what? home assistant you mean the home automation hub?
HA can run as docker container but there is no docker in HA. at least i'd be very surprised.
owrt can too run as docker container but it is not supported as @slh said. it is possible but all sort of problems can happen.
to use image builder check the official doc: https://openwrt.org/docs/guide-user/additional-software/imagebuilder including the prerequisites it requires.
if you mean running HA as docker container on top of owrt that's certainly possible.