You should get a full copy of the pension file. You might find out why there is no record in the rosters. Several reasons:
1. Did he enlist under a different name?
2. Check for mis-spellings. Many names were mis-spelled if the officer was non-German.
3. Verify that it is a Civil War pension. There is an Otto Treptow in the 3rd Wisconsin for the Spanish-American War. This is probably your guy.