I have no idea what the fire ordinance says, and I suspect no other posters do either!! One would have to read the fire ordinance in order to know.
Having said that, one of the main reasons to stay on site is the front of the line access you get with your room card, as well as HP early entry. (We call it the Magic Card!)
Since hotel policy is 5 to a room, you likely will receive only 5 Magic Cards. So, to get 6 Magic Cards, you will need two rooms.
There may be some suites that sleep 6, but it's probably cheaper to book two rooms. Try booking with the Annual Passholder Rate, code is APH. Also, if you are planning to stay three or more nights, they have a stay more play more rate that can be good. Book RPH, which is the cheapest of the three and is about the cost of a moderate motel at Disneyworld. Of course, RPH blows any moderate motel at Disney out of the water. It's gorgeous!