Hi Tom,
It must work,
Try to debug this statement to watch what SQL query is executed and execute it manually in DB.
Working example for CMS.MenuItem page type:
var menuItems = DocumentHelper.GetDocuments("CMS.MenuItem").OnCurrentSite();
is converted to:
exec sp_executesql N'SELECT *
FROM View_CMS_Tree_Joined AS V WITH (NOLOCK, NOEXPAND)
INNER JOIN CONTENT_MenuItem AS C WITH (NOLOCK)
ON [V].[DocumentForeignKeyValue] = [C].[MenuItemID] AND V.ClassName = N''CMS.MenuItem''
LEFT OUTER JOIN COM_SKU AS S WITH (NOLOCK) ON [V].[NodeSKUID] = [S].[SKUID]
WHERE [NodeSiteID] = @NodeSiteID AND [DocumentCulture] = @DocumentCulture',
N'@NodeSiteID int,@DocumentCulture nvarchar(5)', @NodeSiteID=1,@DocumentCulture=N'en-US'