No, not just Dawat-e-Islami, all over the world students are studying Dars-e-Nizami. Yes there are specific books for each subject. For Usuul-e-Fiqh students have to study Usuulush-Shaashi and Noor-ul-Anwaar. For fiqh there is Noor-ul-Eezah,Quduri,Kanz-ud-Daqaiq etc. But some Ulama are teaching other books too.