Are these something we should know for the DAT?

No

Is this definitely true? Cranial nerves are very related to dentistry...

Doubt you need to know them but they are pretty easy to remember if you have a mnemonic. Many of the names are self explanatory and give you an idea of what the nerve does.

http://en.wikipedia.org/wiki/List_of_mnemonics_for_the_cranial_nerves

Here's a list of mnemonics, but I wouldn't worry about this too much for the DAT.

Is this definitely true? Cranial nerves are very related to dentistry...

Indeed. Luckily this isn't a dental board, it's a DAT.