Yes.....otherwise how would any of our phones function? Are you assuming that devs aren't restricted by the same expiration dates? Of course they are - all the date means is Apple will stop signing the first beta by that date so there's no way (unless you have the ipsw's saved) to downgrade.
Much like there are still some people on iOS 5 even though Apple hasn't signed iOS 5 in over a year.
It's not like Apple has some "kill switch" that will render all iPhones on beta 1 useless.
Yea no, the expiration date is a very hard and fast date. On that date/time your phone will cease to function in any way shape or form. You will be required to restore it in iTunes to do anything.