Do not submit a match list. To match into an ob program with intentions of leaving immediately is completely unfair not only to the other people hoping for a match spot but for the entire program you match into.
It leaves the program in a lurch trying to find a candidate mid year and it gives them a reputation of having "residents who leave mid year" which can make it more difficult to match good candidates the following year. No one sees that you came into the program with the intention of leaving because you had decided to do ER before you ever matched.
As far as not wanting to go to a program that has to scramble; there are tons of good programs that are in the scramble every year and if you are flexible on where you want to go it shouldn't be a problem.
Please reread the original post - the OP is currently in an OB/gyn program as a PGY1 and has now decided that he/she would like to change fields, namely from OB into EM. He/she is NOT considering matching into OB for this coming year and then transferring. Sheeesh.
Talk to a PD in EM, or some current residents in EM. There are some EM programs that purposely hold spots outside of the match for people transferring from other fields (I *think* UAB is one such program) - that may actually be your best bet at this point. However, at this time, you will be restricted to programs that routinely do this - the deadline for programs to submit their number of positions available in the match was Jan. 30th, so a program that might otherwise consider offering you a position would not be able to purposely take a position out of the match for you. My hesitation on scrambling would be that you might be so eager to get out of OB and into EM that you may be jumping from the frying pan into the fire without giving yourself enough time to really evaluate programs, evaluate your reasons for transferring specialties, etc.
My advice: 1) Talk to a PD in EM immediately, 2) Start working on a personal statement for EM, 3) Start finding letter writers for a new application to EM (you'll need these if you try to scramble, or if you try to find a position outside of the match), 4) Contact your med school to get your Dean's letter and transcript ready, and possibly your ERAS from last year, for the scramble or for applying for a spot outside the match.