I was actually researching the baby naming ceremony and came across this:
Taken from the OFFICIAL Sikh Rehat Maryada (THE CODE OF SIKH CONDUCT AND CONVENTIONS) published on the Shiromani Gurdwara Parbandhak Committee website:
" k. Persons professing faiths other than the Sikh faith cannot be joined in wedlock by the Anand Karaj ceremony. "
Source:
http://www.sgpc.net/rehat_maryada/section_four_chap_eleven.html