Ok I understand where you are coming from. Correct me if I am wrong but the question becomes three-parted:
1. You get into Simon and get STEM OPT and have 3 years as long as you match the requirements that your STEM degree helps you do your job better.
2. You get into Owen and get approved for STEM OPT thanks to the finance concentration but you end up in consulting or other jobs that are not finance related. So you may be curious if your STEM OPT holds true for the job you have.
3. You get into Owen and do not do the finance concentration so you do not fit the STEM OPT criteria.
So in order to help this problem you want to look at potential employers. Neither Owen nor Simon is a target MBB school so you have to fight very hard for those interviews. However, in my limited research, I think Owen would have EY coming to campus that does sponsor internationals. You may have a slightly stronger network for tech too. So let's look at two possibilities:
1. You get into consulting. Your HR will look at your STEM OPT favorably and often tailor your job description to match the OPT reqs and you will have no issues with the STEM extension if you do not get the H1 lottery. Same applies for tech jobs too. And in the worst case (which is not a bad option at all), you will go to another country (Canada or EU for tech or practically anywhere in the world for consulting) and spend a year or two and come back to the US on the L1 visa - a much stronger alternative to H1s.
2. If you get any job other than tech or consulting it becomes tricky. Your employer can decide whatever they want and it may happen that your finance concentration does not match the STEM OPT requirements.
Anyway, so those are the considerations. Having said that, I would not make a school choice purely on whether they have the STEM OPT option. Is is one of the considerations? Absolutely. But a lot more important factor is whether you will get the job you want - and on that measure, I think Owen wins.