Broadly this is working fine despite me being a newbie to Drupal, PHP and MySQL, with one screw-up.
In G2 standalone the admin a/c owned the top level album, entitled 'albums'. This site will have many users, each owning their own albums. Consequently all user albums are sub-albums of this, so admin can control the settings etc. globally. eg 'albums/Jim, albums/Fred, albums/Mary...' This was set up and worked fine before adding Drupal integration.
However, once embedded, Drupal's admin caused a sub-album called 'admin' to be created ie 'albums/admin'. In other words, admin loses the ability to control all the user albums, 'cos admin now just owns a user-level sub-album.
Unfortunately the embedded control-panel stuff won't let me change this to a null path that would leave admin owning the parent album as I want. I can only set a string which means admin ends up with just an ordinary user album in a subdirectory. Nor can I move the 'admin' album, it stubbornly remains a child of the top level. Gah!
Maybe this is my fault, through leaving 'create a new user album when first accessed' enabled in G2? Too late now, anyhow...
Once I turned off rewritten URL's in G2, I can see what's happening:-
If I'm logged in as admin, G2's 'my album' link points to
http://www.mysite.com/drupal/gallery?g2_view=core.ShowItem&g2_itemId=1293
which is 'albums/admin'.