I think it has a lot to do with the mixed ethnicities of the school. Here at BU, we have a lower population of African-Americans, but a higher population of Asians, and this is reflected in the Greek system here. Despite this, I know here I have never heard of a girl or guy not getting a bid based on ethnicity.
I know in my sorority we are very diverse, with girls of many ethnicities and religions, and I feel just as close to all of them.
As far as Gamma Phi's in other chapters, If I'm remembering this correctly it was awhile back, one magazine(I think it was Seventeen) did an article about this. It profiled 2 sororities, one historically black and the other white, and they both had sisters of the other ethnicity, and how this didn't affect their bond as sisters. I'm proud to say our Alpha chapter was profiled.
If you decide to join the Greek system Mandy, I wish you the best of luck!