This is the place you will be working for. Day in and day out you will be interacting with these people and you will be an employee of this company. You working for this company will be on your resume. Moreover it will be on your conscience.
So with any job, ask yourself: Do the company's goals and morals line up with yours? Don't work for a company you hate, don't trust, or don't enjoy their products. It won't be the job you are best fit for. So if this is concerning to you, and the sources of information seem reputable, I would ask. You either avoid a company who may have legal trouble in the future if its true (which can effect your employment/difficult of job), get a better understanding of the company's response during rocky times, or solidify your enjoyment of how the company does business.
This could jeopardize your employment there if asked in the wrong way. Politely ask them about the situation and ask for their side of the story - do not accuse. Heck! You'll get a side of the story most news sources won't by doing so. If they respond with a nasty response after you've asked nicely - congratulations! I see this as avoiding a company who is unkind to those who question the status quo. If they respond nicely with a reasonable answer, you can rest assured.
There are plenty of other banking jobs! Don't trap yourself into the corner by thinking this may be the only one.