Tapping on the greeting sticker suggestion (added in January 2021) works even if the user has been blocked by you. The user will still receive the message.
The blocked user will receive a message.
Like with ordinary messages, an alert appears asking whether you would like to unblock the user and send the message.
Telegram Android 7.4.2 (22277), Xiaomi Mi 9T Pro, 10 Q (29)