you should know them well..they might give answer choices for GC for example that will all be the same but there will be a difference in s.f. I haven't taken the DAT yet, but that's what I have seen on a few practice tests. After all- sign.figures are very basic...i think you should know them well.
significant figures is like knowing that sodium is a metal if you know what i mean...they obviously won't ask a question about them but knowing that 27x10^4 is not written properly is important imho