Short answer - maybe.
It is suppposed to be for runners, but I have read many accounts of spectators taking the bus there and back. The wildcard is the weather and space. If runners wait to take the later busses to avoid spending extra time milling around, the later busses will be packed and DH might get bumped - if not by the driver, then by runners on the sidewalk.
FWIW, unless he's paid for the primo seats the start is nothing to see. You cannot see your runner and your runner cannot see you. Fire shoots up and thousands of people ooze forward. Not much to look at. If he's going for moral support at some point you'll be separated by protocol. Not sure how fast though.
Is he just going for the start and not going to spectate along the route?
I'm having this delima with DGF, too. Latest plan is for her to take a cab to TTC/MK around 6:00 and catch the monorail to MK from there. I'll drive the car and sit in the parking lot shielded from the wind. I plan to leave 3:15/3:30. You could probably make it leaving later, but I've worked for a year to get there. I'd much rather be an hour early than a minute late. When the gate closes - it's closed. Period.
Good luck.
Ronda