But your users ought to believe it works well to have google's servers respond to the activation link instead of requiring them to click it themselves, so no co

But your users ought to believe it works well to have google's servers respond to the activation link instead of requiring them to click it themselves, so no complaints. The verification process serves only you, the administrator. To everyone else it's a tedious obstacle. Nobody will reach out to you to say "I made it through the registration process just fine but it was slightly less burdensome than I expected, is everything OK?" If you want to know if Google is hitting your activation URLs, check your access logs. Your users will almost certainly not realize it happened. Even if they do notice it, there is no impact on them and no motivation to inform you. You would have to be extremely lucky to hear about it from a user.