If you are using NX 7.5 as the post processor, you can right click on the results item for the first run in the Simulation Navigator and select "Add Companion Result Data". Browse for the .op2 file from the restart run to attach it. Make sure the Append method is set to Create New Load Cases.
Now, if you open the results for the initial run, both sets of results will show up in the Post Navigator. Since the results from both .op2 files are now all grouped under one solution, you can set the post animation to start with the first step in the initial run and end with the last step in the restart run to get a full animation.