To answer your questions,
Yes they are the smartest animal in the woods, next to humans.
30-06 will easily drop any hog that walks the planet, if you place the bullet 150gr or heavier in the neck, or quartering away shot, behind the shoulder. Forget the "head" shot unless you are very, very close. It is easy to hit the head and still miss the small brain.
Yes you can walk up on them if:
the wind is in your favor
you keep the noise level down
you move slowly, as they can hide easier than you might think and you can find yourself in the middle of them when they are bedded before you know it.
have some good snake proof chaps on in S. Tx
wear medium to dark colors if you don't have camo
keep in mind that a sow with piglets can be a dangerous animal, and a boar around a sow in heat is a dangerous animal.
How to distinguish boars from sows?
Sows will likely have piglets or shoats (young pigs, but not babies) with them, likely have enough of a belly to see her teets if she is nursing pigs,
boars when seen from behind have obvious knuts if he is a mature hog. Otherwise it can be difficult.
Vision on a hog is ok, but not their greatest assest. They do pick up motion pretty well though, so go slow.
Their sense of hearing is very good, their sense of smell is tremendous, so don't spit, poop, or take a leak in the area you plan to hunt them.
Few trees in S. Tx to hang a tree stand, so you can use a tripod stand, walk in for them (stay out of their bedding areas), hunt them with trained dogs, bait some holes with sweet feed and corn, spot light at night, etc...
Good luck
markc