I think it makes a difference, but it's up to you how much you emphasize it in your applications. All applications have a section that asks your ethnicity, but I don't think the admission committee is allowed to look at your answer (at least at public schools). If your name is clearly Hispanic, they will realize it, but you can also write about it in your essays or include any relevant information in your CV.
I'm half Hispanic, but I didn't emphasize it in my applications except when they asked for a personal statement about diversity (this was about a quarter of my applications), and my surname is not clearly Spanish. I think that being female might have helped me more as far as getting in. But my impression is that once you're accepted, minority/low-income/first-generation college status can help you win various fellowships.