T.F.
I don't think the weather is that bad but, I have been here since 1989 and I hate cold weather so the heat does not bother me. I am sure it would bother some people but I don't think we have the humidity that you do in VA.
Where is the wedding venue and what area of town will you be staying? DFW is so widespread.
As for August, I don't know specific things to do because we do things all the time. You can google and check if there are any special events at anything I might suggest.
Zoo, Dallas Aquarium (West End area), Arboretum, Clyde Warren Park downtown Dallas, Ft. Worth Zoo, Ft. Worth Stockyards, Mesquite Rodeo, Northpark Mall (best shopping), ice skating at the Galleria, Reunion Tower, Rangers or Frisco Roughriders baseball game, Gaylord Texan is fun to go through and would be in air conditioning as well.
We have excellent high quality restaurants if you want any info on restaurants.
I hope you have a great trip!! Feel free to PM if you want any details on something.