Maintenance Mode only effects alarms, however reports are often showing data such as % of CPU and so would be unaffected by maintenance mode.
Absolutely the data can be pulled from the database via query.
S_QOS_DATA is the first table to look at with a kind of address book to the other tables that have the data. It lists the 'source' which is the system being polled, the qos which is the metric, the RN_QOS_DATA_ which has the data for that qos metric, and the table_id. The data in the RN_QOS_DATA_ tables is identified via the table_id which is specific to that source & qos.
Just from my notes and not providing exactly what you want and given just for a starting point.
select * FROM S_QOS_DATA where source = '<system name>'
select * FROM RN_QOS_DATA_xxxx where table_id = 50684 and sampletime > '2015-11-24 10:15:00' order by sampletime desc
but you would want a sampletime that is both less than and greater than.