It should have worked, but there's a couple of possibilities.
- Sometimes, you have to restart UE before actually importing a map after importing a bucketload of materials, since it takes it a while to catch up on the new files.
- Did you check that the material assignments on import were correct? (If they weren't, you might have to rebuild the master list in the discovery section of the TextUEr tab)
- Another possibility might be that your material might have some kind of problem if you're not using the supplied one that stops UE from rendering some combinations until the problem is fixed.