There are soooooo many people that ride the MS you're basically never alone. Yes there are teams or groups that will pace-line and roll like crazy, and you can try to hang with them or get a group of your own. These riders will be out front the whole time mostly so you need to ride early. These are the guys who get to the lunch stop at like 10am, and are done by noon - while the rest of the 10,000 people finish between like 2-5pm.
Basically, there will always be a group of people you can draft either going at every speed imaginable.

Many of the fast-riding pace lines also end up riding out in the road to go around everyone instead of staying on the generously sized shoulders.

Just be prepared because even though this isn't a race, many, many people treat it like their very own Tour de France, and will ride like dicks.