I am pleasantly surprised that you are asking what I thought you were asking.
It depends on how you ask. Strictly speaking, the set of raw files that will not be ignored by DF or cause error messages in DF is not regular. For example, if you have an interaction that turns you into a creature or caste that does not exist, then it will cause an error message. The name of a creature or caste (DWARF, ELF, COLOSSUS_BRONZE, etc) can be arbitrarily long, and a DFA cannot remember the entire thing, and thus cannot know for certain whether that creature exists or not. Technically this makes them not even context-free, because the set of all strings of the form {x x} where x is some string is not context-free.
Ignoring such issues, and looking at the raws, I'm surprised to say that I think most of it is regular. There are finitely-many tags, numbers are not an issue, and there are finitely-many "contexts", such as defining a creature, listing something like
[TL_COLOR_MODIFIER:IRIS_EYE_AMBER:1:IRIS_EYE_AQUA:1:IRIS_EYE_AQUAMARINE:1:IRIS_EYE_ASH_GRAY:1:IRIS_EYE_AUBURN:1:IRIS_EYE_AZURE:1:IRIS_EYE_BLUE:1:IRIS_EYE_BRASS:1:IRIS_EYE_BRONZE:1:IRIS_EYE_BROWN:1:IRIS_EYE_CERULEAN:1:IRIS_EYE_CHESTNUT:1:IRIS_EYE_CHOCOLATE:1:IRIS_EYE_CINNAMON:1:IRIS_EYE_COPPER:1:IRIS_EYE_DARK_BLUE:1:IRIS_EYE_DARK_BROWN:1:IRIS_EYE_DARK_CHESTNUT:1:IRIS_EYE_DARK_GREEN:1:IRIS_EYE_DARK_OLIVE:1:IRIS_EYE_DARK_TAN:1:IRIS_EYE_ECRU:1:IRIS_EYE_EMERALD:1:IRIS_EYE_FERN_GREEN:1:IRIS_EYE_GRAY:1:IRIS_EYE_GREEN:1:IRIS_EYE_JADE:1:IRIS_EYE_LIGHT_BLUE:1:IRIS_EYE_LIGHT_BROWN:1:IRIS_EYE_MAHOGANY:1:IRIS_EYE_MIDNIGHT_BLUE:1:IRIS_EYE_OCHRE:1:IRIS_EYE_OLIVE:1:IRIS_EYE_PALE_BLUE:1:IRIS_EYE_PALE_BROWN:1:IRIS_EYE_PALE_CHESTNUT:1:IRIS_EYE_PERIWINKLE:1:IRIS_EYE_PINE_GREEN:1:IRIS_EYE_RAW_UMBER:1:IRIS_EYE_RUSSET:1:IRIS_EYE_SEA_GREEN:1:IRIS_EYE_SEPIA:1:IRIS_EYE_SKY_BLUE:1:IRIS_EYE_SLATE_GRAY:1:IRIS_EYE_SPRING_GREEN:1:IRIS_EYE_TAN:1:IRIS_EYE_TAUPE_DARK:1:IRIS_EYE_TAUPE_GRAY:1:IRIS_EYE_TAUPE_MEDIUM:1:IRIS_EYE_TAUPE_PALE:1:IRIS_EYE_TAUPE_SANDY:1:IRIS_EYE_TEAL:1:IRIS_EYE_TURQUOISE:1]
etc.
That being said, if you really want to parse them, you'd probably have a much easier time of it if you do it in a context-free way.