Does View UI restrict fields based on filters, etc In the Views UI, are the fields that you can add restricted by whats possible due to the filters, contextual filters, relationships etc? Eg if I set a filter to node type A, will the ui allow me to add fields that only exist in node type B?
In Views 3 in Drupal 6, the UI does not enforce any restriction of fields. (And it does tell you what content type(s) the field exists when you want to select one).  About the only restriction I can think of is the initial View type, eg, a node View restricts you to nodes, taxonomy restricts you to terms, users to users, etc.