None of the marking scheme of public exams that I know of has anything on marking down or up the candidate's pronuncation because of the different accents of English he/she speaks. Whether you are talking about HKEA or IELTS or TOEFL or whatsoever.
Candidates are only marked down if they CANNOT speak "fluent and spontaneous" English or their accent is absolutely "UNINTELLIGIBLE".
A good example of unintelligible English is to speak English with a South African accent. Want to know what it sounds like? Watch Leonardo DiCaprio in Blood Diamond.