Well - I didn't respond before because you appeared to want very much specifics - but here's what I know.
I've never heard of companies #3 and 4. I don't personally have an interest in research, so I don't know what connections they might or might not have to Emory and CDC. There are certainly multiple rotations available at Emory and at CHOA - Egleston, and I know we have at least one faculty member whose primary clinical site is Emory University Hospital.
We also have an on-campus clinical research facility, and two faculty members whose primary work is with that. The head of the clinical side of the faculty also has extensive experience in the research side of things, primarily psychiatric. And, we also have pharmaceutical faculty who are conducting more primary-type research - I have several friends who have done either a research elective class or summer internship experience with those faculty.
Mercer also has very close ties with Solvay Pharmaceutical in Marietta - they have numerous rotations and also offer paid internships for several students every summer.
So, that's just the things I know about from my friends - but the bottom line is that clinical and research experiences are, in my opinion, easy to get involved with at Mercer if you are so inclined. As I'm sure you know, we also have a joint PharmD/PhD program for those few students who are really hard-core for pure science research.
I'm not sure who you contacted on the faculty or what your status is (applicant, accepted, or what), but I am sorry that you didn't get a good response. In general I have found faculty at Mercer to be very responsive to students. PM me if I can answer anything further.