MIT is known to be a very open university (i.e. anyone can walk in, use the libraries, sit in for a lecture etc...) So given that nature of it, it would be very unlikely for this event to be limited to a small number of MIT people.

Also, Startup Bootcamp (http://startupbootcamp.mit.edu/) is a well known event held at MIT that doesn't require you to be affiliated with the school in any way, so I doubt this would.

I have the same question but seems like its free and anybody can go. Gary's blog does not post any restrictions either.