WDW busses operate early for these breakfasts, tours, etc. The MK area busses start before 6:30AM. The epcot, MGM and AK area busses (separate busses for each area) start about 7AM.
So, no you don't need to get a cab. As an FYI, the AK parking lot typically does not open until 8:30AM, so you ouldn't be able to get in. However, AK may be changing their policy since I read here on the DIS that the parking lot opened at 7:45AM on May 6.
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