What you're asking about is a term that attorneys call "standing:" that is, you have to be affected by the defendant's acts in order to sue the defendant.
I don't know what Somos America claimed was sufficient to constitute its standing. Its website states that it's an organization "composed of organizations and individuals whose work encompasses issues affecting immigrant communities."
I can theorize several bases on which they could claim standing. Racial profiling causes disproportionate numbers of their members to be arrested, making their work more difficult. That's the first thing that comes to mind.
Standing doesn't require a great deal of harm to be experienced, especially when the plaintiff is seeking injunctive relief.
Thank you for your thoughtful question.
Craig T. Byrnes
Disclaimer: Please be aware that I am not offering legal advice, nor forming an attorney-client relationship with you. I am not representing you, nor doing anything to protect your legal rights. If you believe that you have suffered a legal wrong, take action before any statute or limitations expires, or your right to do so may be lost forever. Good luck in your legal matter.
A LOT of different groups like to put their "two-cents" in where
there is a controversial or well known law suit pending. You see
the Small Business Manufacturers and MADD and others do this
all the time. Somos America wants their "views" aired re: "racial
profiling" to be known. That's why.
THIS ANSWER IS PURELY FOR ACADEMIC DISCUSSION ONLY AND DOES NOT CONSTITUTE ANY TYPE OF LEGAL ADVICE OR LEGAL REPRESENTATION.