I got married June of 2011, and it was 103 on my wedding day. Even if I would have held my ceremony at 7 or 8 to try and beat the heat, it would have only gotten down to maybe 95 and people still would have been miserable for my guests. I wasn't able to take any outdoor photos because my face would have melted off. Even inside the Church, I was hot despite the AC blasting--my dress probably added to it (that fabric is heavy!), but I spent a good portion of the time that we waited between pre-ceremony pics in the bridal suite in front of a fan.
I really wouldn't recommend an outdoor ceremony to anyone in TX after April or before October since the heat can really get bad and is totally unpredictable. It might not be a sweltering 100+ degrees, but you really have to think of your guests comfort (especially children and the elderly).