The MCAT bio and DAT are really different from each other. MCAT has quite a few topics not on the DAT, but the DAT has quite a few topics not on the MCAT.
The DAT bio follows the topics covered in pretty much every undergrad school's 1 year pre-dental/pre-med bio requirement. While the MCAT is a different beast and completely gets rid of things like evolution, ecology etc and replaces it with physiology and a few other topics that most people don't cover in their 1st year of college bio.
The Kaplan MCAT and DAT books are identical in the General Chem and O. Chem sections. While bio is different, and DAT omits physics but adds quant, and PAT. Reading Comprehension is a completely different story between the two tests - the DAT being much easier.