Getting an assistantship does not preclude the awardees from getting an additional scholarship.  The scholarships are only available for new students:

Dean’s Scholarship:             $1000/yr for 2 years (MS) 
                                           $2000/yr for 4 years (PhD)
Subject to be renewed on a semester-by-semester basis as long as the GPA of the awardee remains at or above 3.0.

MSE Department Scholarship:  $1000/yr for 1 year.

• Student awardees of Assistantship and/or Scholarship are treated as residents of the State of Texas, eligible for reduced rate of “in-state” tuition. 
• Assistantship/Scholarship Selection Criteria: 

Candidates are evaluated based on the following criteria: GPA, Research excellence (papers, presentations, reports, etc.), recommendation letters, and GRE score.