Who is your reseller? They are completely wrong.
The new naming conventions should make things simple: Revit data can be exchanged back an forth only between the same versions, in this case, r2008 of both Revit Structure and Revit Architecture.
Of course, you can always open older versions or Revit files in the latest version- but once that data is upgrade, there is no going back. If you followed your reseller's advice, with you working in 9.1 and your structural engineer working in r2008, you would not be able to re-import his data into your file in 9.1.
Joe