Are there any rituals, ceremonies, or holidays in which a non-Sikh would be precluded from participating in?
A non-Sikh cannot lead any Sikh ceremony or congregation. He can take part as an attendee in some ceremonies. In case of Amrit, he cannot be a part of it unless he is receiving it. In Anand Karaj, he cannot have this ceremony because he doesn’t follow the Sikh way of life. Any person can come and sit in the Gurdwara and attain spiritual benefits. However, non-Sikh ceremonies and practices cannot be performed in a Gurdwara.