Now, are you asking about the residents that go to the pre-interview dinner or the residents that may interview you during interview day? I think either way, this depends on the program and even the specialty that is in questions. I know last year when I was a prelim in an IM program, I was asked to interview applicants. Usually this would be during my work day and so I wouldn't have too much time to see the application of the person that I would be interviewing. Usually, I'd come into the PCs office and take a file... then look through it for a few minutes to get the basics of the applicant (i.e. school, scores, LORs, publications, interests) and then go in and ask the person questions for a 10 minute interview. At the end we'd fill out a questionare and put in our input on whether this applicant should be ranked highly, low, not ranked at all. I'm not sure how important or if at all were the resident's comments used.
Still, I think that usually, the residents that are present during the pre-interview dinner or during the lunch during interview day have little say on whether an applicant gets in. Mainly I think they're asked if the applicant in question seems like someone that they can work with and is generally a good person to be around. Still, if you act weird or say something that you're not supposed to to the residents, I guarantee that it will get back to the PD.