Night buses aren't specifically excluded, but the national scheme only allows travel (as in journey starting) after 9.30 am and before 11pm on Monday - Friday. So night buses might be OK on Saturday nights. I'm not sure how Friday or Sunday nights work...
I appreciate there's got to be a cut-off somewhere before the morning peak starts, for the few places that have all-night services (think Transport for London regard each operating day as starting / ending at 4.30 am) but why the government at the time thought that concessionary pass-holders ought to be at least on their way home before pub closing time, I've never quite understood...
Some councils extend their scheme beyond the statutory hours, either all day, or start from 0900 or whatever. (There are also a few local exceptions in some places where there's a very infrequent bus service where individual journeys start before 0930.) - this will apply where the journey happens (and may only be for local pass-holders) so if X council allows travel during the morning peak, it only applies locally - an X Council pass-holder can't travel during the morning peak somewhere else.
There are a few exceptions - as has been mentioned, open top tours are generally excluded, some services for special events, or football match shuttles are also excluded.
And yes, it's England - the four countries of the UK have their own schemes, and (there may be exceptions on services that meander around the borders) you can't use a pass from one country in another.
In some places, concessionary passes can be used for free or discounted travel on things like metro / trams / underground / local rail services, but this is also discretionary, not part of the national scheme - and may only apply to people who hold a local pass - last time I had cause to think about it, the Nottingham trams (for example) could be used by Nottingham / Nottinghamshire pass-holders but not pass-holders from anywhere else (it may have changed since then.)
One other thing - if you travel in London, then you show the pass to the bus driver rather than try and beep it on the ticket machine - the ticket system in London was quite advanced a long time ago, but is now so old it doesn't meet national standards.
Happy travelling.