You can get a count of 0 by including 'ME' in the data set you select from:
select owner,table_name,count(table_name)
from (select owner,table_name from all_tables
union all
select 'ME',null table_name from dual)
where owner = 'ME'
group by owner,table_name
/
ME 0
But be careful: count(*) counts the number of records. Because there now is a record with owner='ME' you'd get a result of 1. You get 0 because table_name is null in that record.