How safe is Poland for foreigners? Do you see Chinese, Indian/Pakistani, Africans etc.,

I think its safe. It is a city, so basically every city in the world has crime. Knock on wood I have never been mugged or robbed and am on my 3rd year. Very few of my friends have been robbed. It does happen, but its usually their fault. Just use common sense. Don't carry thousands of dollars on you. Even when I walked around the town center many times at night (and night is like 3am) I never was even stopped. I have a few classmates that do stick out as a foreigner, and they never had any problems.
One thing though there are burglaries in the apartments over the summer. It happened to a few classmates. Once again, they let themselves known by renting nicer apartments will all foreigners in the building. Just use some common sense. Its a overall safe city. Take London for instance. You'd be amazed how much pick pocketing goes on in that city. I would say a lot more than Krakow.

Does JU have any history of crimes against foreign students?

Not sure I understand this question. The actual school? No. Well, Krakow is a student town with over 250,000 students I believe, so can it happen you get pick pocketed by another student if that is what you meant.