I think "additives other than commercial beer are okay" applies here but that's my opinion.
According to the rules on Special Ingredients Instructions on page 6 of the 2011 NHC Rules and Regulations.
Special Ingredients Instructions
Entries in categories 6D, 16E, 17F, 20, 21A, 21B, 22B, 22C, 23, 25C, 26A, 26C, 27E, 28A, 28B, and
28D require Style and/or Special Ingredients information. As a general rule, these ingredients must
play a role in the overall flavor/aroma/mouthfeel of the homebrew. Conversely, a homebrew listed in a
category not requiring special ingredients, should not have any special ingredients listed.
All MEAD entries (categories 24, 25, 26) must include sweetness, carbonation, and strength
All CIDER entries (categories 27, 28) must include sweetness, and carbonation information.
If the required information is not provided, the entry will be disqualified.
Please do not use brand names, or geographic names, or any other proper names of special ingredients.
For example, if you used Premier malt extract, Briess pale malt, Washington apples, Colorado clover
honey, or Sitka spruce tips, only enter malt extract, pale malt, apples, clover honey, or spruce tips,