Having a TX DL is not a requirement. All I needed to prove residency was my mortgage statement, banking statement, and utility bills in my name and address.Interesting. They're supposed to require a Texas DL - since the LTC card is accepted as proof of residency for voting.
I know that there are out of state residents who also have a TX LTC, residency is not a prerequisite to hold one. A few that I know of are Lousiana residnets who visit the state on a regular basis.