Is written Hakka the same as simplified Chinese?
I have an old Hakka textbook, published in Singapore in the 1950s. It is written in transcription (for the learner) and in Chinese, using Traditional characters, including some Hakka-specific characters -- borrowed most probably from Cantonese -- like 冇, 唔.

Below are a couple of pages. Today, though, it is rarely written, and when it is, the writer will use whatever character set he or she uses for Mandarin.