A) If the umpire calls the pitch a strike, there is no appeal in any way shape or form. Why is that, you ask?
Because if you did not see the ball pass through part of the strike zone, or did not see a swing, you would have called it a ball. Like outs, strikes shouldn't be "guessed". So, if you called a pitch a strike, you saw a strike and/or the batter swing.
Going for help on a swing/strike call is acknowledging you do not know what you are doing behind the plate.
B) A base umpire should ALWAYS offer what they saw. Again, if unsure of the alleged swing, the BU should offer a "safe" signal with a verbal "NO".
C) ASA does not require the PU ask for help upon request, but indicates a PU that is unsure of a swing SHOULD go to the BU for help (ASA Umpire Manual, page 221
).