custom module to display content (nodes and fields) from another database
Absolutely you can use a different db for a view. First create a custom module use hook_views_data() in a .views.inc file to define the fields of the external db. Once you have defined the fields and cleared the cache you will be able to select a different base table for your view.

With some custom coding and db_set_active() or views relationships you should be able to use both.

EDIT: Assuming Drupal 7.