My copy that I was looking at maybe a little out of date (1999)
But it clearly shows in there that SSID is a required field in the beacon frame.
Having said that most vendors have relized the limitations of this and give you the option to turn it off and a lot of cards will work fine if this is not broadcasted.
If you want your AP to be configured strictly to the standards leave it on (default) if not you have the option to turn it off
Does this answer your questions