To answer your question. No they do not open earlier if there is a morning EMH. The character breakfasts at MK, DHS and AK all open at 8am, every day. I always seem to get a 8:05 slot. The Princess breakfast at Epcot starts seating around 8:30am.
A CM is on hand to let you into the park (before opening) to get to your restaurant. They usually have a clip board with the ADR names on, so they will check to see if you are on the list. They will usually allow you in around 7:50 - 7:55 to get to your breakfast. Don't panic if you don't think you are going to make it. They do make allowances for this. As you are the first ones that day, and the park isn't open your table is not going to be given away to a walk up. However you probably don't want to be rolling up a half an hour late.
There is early morning transport. We have always been able to use the monorail that early, or resort buses. Allow a little extra time for the buses, as they aren't that frequent. I would say maybe every 20 minutes. The Epcot branch of the monorail was not open one time we were going to The Princess breakfast, however there were CM"s directing you to a special bus. It's a bit of a trek to Norway, so allow the extra time.