Yes,Urdu is compulsory for applying in b.u.m.s Students must read urdu upto 10th class. As the entrance tests comprises of 2 papers, Paper 1 of Physics, chemistry and maths and paper 2 of Urdu and General knowledge. So it is compulsory for a student to know urdu so that they can qualify the entrance exams easily.
And diploma is done after 10th so I think you will be Eligible as u must read Urdu till 10th.
Hope this helps you
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All the best for your future