I don't know how well OU places in Dallas (as I am an SMU Law alum), but based on my PERSONAL legal experience here in Dallas, I haven't seen as many OU lawyers as I expected. I don't know if it is because folks from OU aren't interested in Dallas or if it is too hard for them to find a job, but there are definitely more Texas Tech lawyers than OU lawyers in Dallas.
I posted this link a few months ago, but here is a list of the "top 23" law firms in texas and which law schools their entry level associates went. This list includes law firms all over Texas, but it's probably an even split between Dallas and Houston.http://www.lawschooldiscussion.org/prelaw/index.php/topic,4016101.0.html
Also, you can conduct a search on MartinDale using the "Advanced Search" criteria and try and find the number of lawyers who graduated from OU and practice in Dallas. It would probably be best to hone in your search to lawyers who have been practicing for less than 5 years, as that number would reflect how many recent grads are in Dallas.http://www.martindale.com/Find-Lawyers-and-Law-Firms.aspx
The best resource for you would probably be utilizing the Career Services Office at OU and ask how many of their newest graduates found jobs in Dallas compared to the graduating class. I'm not sure how secretive those offices are to prospective law students with their numbers, but they should give you an honest answer as to how their graduates are doing. Also ask them what class rank the students who move to Dallas usually have and see if those people had a connection to Dallas before law school (i.e. family lives there, they went to undergrad their, Dallas was their hometown, etc).