Interestingly, I was Thumbing through the hunting regulations and a pellet gun is a legal weapon for hogs. It even specifically states pellet rifle.
Since hogs are classified as "exotics" in Texas nearly any means are legal to take them (I.E. any legal rifle, Pistol, Bow, Knife, Spear, snares,Helicopters,Rocks, Pipe wrenches, what have you). They can be hunted at night with the aid of lights (private property) there is no bag limit or season (hunt them anytime, as many as you like).
If you can kill one with a pellet rifle, sling shot, blow gun or with your bare hands...the State of Texas doesn't care...and encourages land owners to reduce the number of Feral Hogs.