Do you know if the Satmar Rebbe, the Hatam Sofer, or R Hillel Lichtenstein wrote books in Yiddish? Do you know if Shirat Moshe by the Hatam Sofer is written in Yiddish?
I am also looking for rabbinical books in yiddish with vowels. Do you know any?
I don't know of books in Yiddish by the rabbis you mentioned offhand, but there are many rabbis whose Yiddish-language speeches were collected, naturally, in Yiddish. Most famous of these is probably the many, many volumes of the Lubavitcher Rebbe's sichos. You will have a hard time finding Yiddish books with Hebrew-style vowels because Yiddish uses a different convention where Hebrew consonants represent vowels. Broadly speaking, ע=eh א=uh or ah. Hebrew nikkud is only used in Yiddish for ambiguities.