I am new to all this but how cold hardy is a pitcher plant
Forget having one outside in winter in Dallas. It gets way too cold there. Matter of fact, the heat might be too much for them as well. If you want something you can leave outdoors over winter, I'd focus on the North American species like vft and Sarracenia. There's probably some sundews and pings that would do OK as well. Either way, any plants outdoors are going to go dormant during winter.
are all of the Sarracenia hardy to the texas winter/summer?
Sarracenia are hardy by zone, here in zone 6 i have to provide overwintering protection but since you live in zone 8, i dont think you would need too. Most sarracenia will tolerate 80-100F during day 60+ at night although i havn't experienced temps above say 95F here.
As for nepenthes, yes they are my favorite and if you would like to grow some you can just depends on which plants you choose, there are highland and lowland nepenthes. Highlanders prefer day temps to be 70-90F and have cool night 55-65F, lowlanders like it hot and humid through the day and night, so 80-90F, they are tropical plants and wont overwinter outdoors but you can bring them inside and grow them as a houseplant while the winter passes. i grow my neps in partial sun, mist them daily, and keep there soil moist at all times, if temps are high you have to water more often, low, not as much
I believe there's some Sarracenias that grow wild in Texas in the swampy areas along the coast.