List databases in Maintenance Plan
-- This seems to be close to I think what you are needing 
-- shows dbs not in a maint plan (run pointing to msdb)  
select
t1.name as 'db_name',
--t2.database_name,
t1.crdate as 'date_created'
FROM [master].[dbo].[sysdatabases] as t1
left outer join
dbo.sysdbmaintplan_databases as t2
on t1.name = t2.database_name
where t2.database_name is null
and t1.name not in ('tempdb','msdb','model','master')
order by crdate desc