Guide or pass necessary to go into Antelope Canyon?

Totally correct. There are many slot canyons in this area, and most are either inaccessible or on Indian land, such as antelope canyon.  We were in Page, as two months ago.  We saw the tours for antelope canyon lined up like cattle headed to market.

Suggestion: We went to Waterholes Canyon... a slot canyon in the area but visited by very few people.  Only one tour operator has permission from the Indian family who owns the land.  Www.hummeradventures.net.  Antelope Canyon is around $50 per person and you are in and out in 45 min. 14 tour operators have permission here.  Water holes canyon is pricey.. $125  per person.  But you get an incredible 3 to 4 hour trip through the desert in a hummer ..not for the faint of heart.  When you get to the slot canyon, you and the maximum of 5 people they take per tour have the canyon to yourselves, along with guide who is invaluable.  The slot canyon is awesome; the experience is incredible. It is Completely Worth the price difference. The 3 to 4 hours includes the time in the canyon, and the pickup point is in Page, AZ, or they will come to your hotel if you are staying locally. 

Yes you will have to get a guide unfortunately. And they stay pretty close

Absolutely have to go with a guide. It is totally controlled by the Navajo nation.