texas hunting law question ?

Simple answer for recreational hunting even pests and none game animals is yes you do have to have an hunting license.
Really the only exceptions to this is if you are a land owner who is removing the vermin because of property damage of one sort or another, or you are employed by the land owner to rid the vermin for him and are doing so not for yourself but only for the land owner.
Just saying I'm helping the land owner out by getting rid of the pigs won't do you much good if you don't have a license.
Don't know the price for an out of state license and if your only gonna be hunting in this state for a short period of time, you can probably get a two week license instead of one that spans the hunting season. If Texas offers a short term hunting license.