You are correct about some places allowing single-driver HOV lane access, but Texas is not yet on that list.
The Texas Department of Transportation website states the traditional rules—i.e., two or more passengers—and includes a list of conventional vehicles allowed to use the HOV lane. But the site makes no mention of any exceptions for EVs.
A few years ago, there was an online petition for Texas to change its laws, but it has not yet had much of an effect on legislation. The laws may change if Texas wants to push for electric vehicles, but so far, they haven’t.