I don't think the prematriculation program at UTSW is research based. Most premat programs are more for enrichment, with a brief exposure to the courses you will have during your first year.
As far as research, there is always going to be the opportunity to do it. The summer before my first year I moved to Houston and worked in a neurobiology lab. Looking back on it, I really got nothing meaningful from it, except for brushing up on my gel-making and radionucleotide-handling skills. However, if you have money saved up such that you could live without working, I would suggest enjoying the summer. In the middle of my research, Houston flooded and my project was put on hold for a month. I went to Galveston, kayaked almost daily and really enjoyed having the time to be free. You'll appreciate it in October-November when you are sick of not having had any time for yourself.