Check out rule 13.5.A on page 73 of
the Rule Book
I'd say that you are allowed to go with more than one adjuster by the rules. However, if you don't know this already, my guess is you are not experienced enough for a double adjusting damper. It isn't as easy as a single adjuster and can cause bigger problems having to tune 2 things.
My suggestion would be to go with a single adjuster just because it is simpler. Especially for a National level autocross, you won't have the time to think and adjust multiple things, so eliminating options is generally a good thing for a rushed format like that. Road racing allows much more time to analyze and think things through, so if you have the pockets to afford some test sessions, then the double adjusters might be better.
Just my 2 cents though. Others will probably disagree, but we each have opinions.