There is racism here as there is everywhere. However the university is massively multicultural and thousands of students of all races graduate every year unharmed. In most of my classes there must be at least 30% international students - higher and lower in other courses. At uni its very unlikely you will encounter racism (in my opinion anyway), the university is extremely tough on racism so if you have any problems its likely they will be dealt with sharpish! They are also very proud of welcoming international students.
Outwith uni there is racism but generally what you find is that any aggressive/violent behaviour is mostly confined to the very rough areas. It is similar to any other aggressive behaviour. I am white and scottish but i got shouted at in the street by a bunch of horrible yobs because i was wearing a suit, as i had visited a friend and hadn't changed after work! So they shouted at me because they thought i was rich/stuck-up/who-knows-what! If you are african you might get shouted at for that, if you old you might get shouted at for that! etc etc! (I will add in my 3 years of living in aberdeen, such an event has only happened once. I have an indian friend who has been here for 4 years and never had a problem.)
Its the same as in any other city. There are idiots, small minded fools who only want to cause trouble. There are also friendly welcoming people who dont care about race, where youre from or what your background is. Racism in aberdeen is certainly not as bad as the article makes out, where non aberdonians cower in fear after dark. Also question the reason for people are reporting to the police - maybe there is worse levels of racism in other parts, but in aberdeen the police are particularly helpful and supportive. I dunno, but i certainly wouldnt base a decision of whether or not to come to aberdeen on this one issue.