Can guests scan this Wi-Fi QR code with the standard iPhone camera?

Yes. Both Apple's iOS Camera and QR Code Reader & Generator recognize the standard WIFI:T:WPA;S:...;P:...;; format and prompt the user to join the network in one tap.

Is my Wi-Fi password stored or transmitted anywhere?

No. Your SSID and password are encoded into the QR matrix strictly inside your browser using local JavaScript.