In 2005.. i know 2 people who got auto-kicked out of nrmp match like on 20th of Feb because they have not passed step 2 yet. I presume the same system remains the same. If you are waiting for results still by the time the match starts, most US schools will try to scramble you anyway when the scramble is up, even if you didn't participate in the match. Hence some people begin residency and have not passed step 2 (getting more rare from what I hear).