It's a bit hard to tell. Unlike UoN, NTU doesn't seem to make public its student breakdowns, or if they do, they're not too easy to find.
It depends somewhat what subject you plan on studying. NTU do publish a report which comments on ethnicity (this year shows them a few percentage points above the sector average for percentage of students identifying as BME), which can be downloaded from
http://www.ntu.ac.uk/equality_diversity/document_uploads/117416.pdf. Some departments will have more BME students than others, but they don't provide a specific breakdown by ethnicity, fee status, or department.
DMU's data is ridiculous to comprehend. It's neither comprehensive or clear, but if you want to read their 2010/11 report, it's at
http://www.dmu.ac.uk/documents/about-dmu-documents/equality-and-diversity/equality-information-january-2012/sps3290studentdiversityreport2010-11v5forinternet.pdf.
I guess what I'm getting at is that I wouldn't pay too much attention to it. The two universities will be very similar in terms of diversity, particular if we're talking about culture, ethnicity, and home country. Both will have a very diverse student body and there will be plenty of opportunities to experience other cultures, get involved in a variety of activities, and developing an international perspective to what you learn.
Both cities are fairly diverse also.
One thing to note is that NTU students can apply to be Associate Members of University of Nottingham Students' Union if you wanted to join one of our many cultural societies:
http://www.su.nottingham.ac.uk/activities/societies/religiousandcultural/