If they ask you to play, then play. I do not see why your choice in songs is relevant at all. The interesting point about playing an instrument, at least from an adcom's POV is that you are able to take time out of your daily life and dedicate it to a passion you personally have.
To go more in depth, while talking to an adcom member from my school several months into my first year, he brought up the topic of playing an instrument and how relevant it is to being a well-rounded physician. It is a mechanical process of selecting the chords, it is an intellectual process, of understanding the music and the progression of the song, etc, and it is an emotional process, whereby you are trying to create music. He likened it to the anatomy labs, whereby you must dissect, understand anatomy, and understand that you are cutting into a former human being. Again, the three categories of mechanical, intellectual, and emotional stimuli working in unison.
Of course, playing an instrument was not the only thing which qualified as meeting this requirement in his mind, but it is a common example.
Now then, on to personal experience with interviews:
I listed I played the violin. I was asked in every interview about how long I had been playing, why I started, what I enjoyed to play, etc. My response would always be "I sort of lied... I don't play the violin, I would rather call it a fiddle" and expanded on how I enjoy bluegrass, cheesy celtic nonsense, and pretty much despised classical music. That was always very well received, and one school shared with me that they apparently had a faculty-only Charlie Daniel's cover band.
So, if you play the guitar, you play the guitar. Your music selection should not matter. You're not interviewing for Julliard.