The letter from TPWD helps quite a bit for some,
Nongame and Other Species
NONGAME ANIMALS (Includes, but is not limited to the following):
EXOTIC ANIMALS AND FOWL Exotic animal
refers to grass-eating or plant-eating, single-hoofed or cloven-hoofed mammals that are not indigenous or native to Texas and are known as ungulates, including animals from the deer and antelope families that landowners have introduced into this state. Includes, but is not limited to feral hog, Aoudad sheep, Axis deer, Elk, Sika deer, Fallow deer, Blackbuck antelope, Nilgai antelope, and Russian boar.
Although the Warden said that feral hogs are considered/treated as exotics, they still fall under non-game species.... just as Axis, Aoudad, Sika, Elk, etc. are considered Exotics, they'd be considered non-game (same section of the law as feral pigs, and assuming that the Warden understands it as I do, that means silencers for those types of animals as well).
There is a company/outfitter in East Texas (Tactical Hog Control) that offers suppressed night/thermal hunts... so it's more than obvious a company like that can be doing that for a living, and being perfectly legal at the same time.
As the warden said, keep all NFA paperwork on hand, and for those travelling with NFA items, ALWAYS check with BATF prior to crossing state lines. That should be a moot point however, if you own and possess an NFA item.
Long Live Texas.... and Long Live Liberty!