for govt funded primary-secondary, yes, there's dragon schools.
however, in the present system, govt funded primary cannot select their own student, i.e. even there's a KG of same organization, they cannot bypass the govt system and accept their own student.
for private school.. there's one called united christian school.. it's a international school.
in shatin area, there's only two DSS. for the BU school, they have preference to their own KG graduate (KG in kln tong). however, there's a limit on shatin residence.. i think upto around 10-15% intake only. so, the competition in shatin area would be keen.
in Tai wai, over half of the school have there seat filled in P1 round 1 allocation. and 張煊昌 primary is one of those which still have seats not filled in round 1.
i.e. you dont need to be their KG's graduate, you just need to apply this school in round 1, you will have their offer.
btw, one-dragon is only for primary to secondary. it's not applicable for KG to P1 in this case (as the primary is govt funded).
and... 張煊昌幼稚園 is in ma on shan.. Primary in tai wai and secondary in ma on shan too.