In Mail.app are images for a gmail account pulled from google image proxy servers or original servers?
Apple's Mail.app fetches email over IMAP. Gmail does not replace any image URLs when email is accessed through IMAP, therefore images come directly from the original source.

You can verify that by reviewing the raw source of the email in your IMAP client (e.g. Mail.app). Select View > Message > Raw Source from the menu. Alternatively, use the keyboard shortcut Option-Command-U.