Freezing increases level of thiaminase in foods, thus reducing the thiamine levels over fresh rodents. So supplementing B-1 would be a logical choice. Brewer's yeast is a good source of B vitamins.
http://animal.ifas.ufl.edu/courses/ans6449/Thiamin.htm
(Note the loss of Thiamine in frozen meats over time)
http://books.google.com/books?id=6ry...um=1&ct=result
Can you feed f/t rodents without supplementing thiamine and have healthy snakes? Sure. But since Thiamine does affect fertility and nervous system function, and IS reduced over time in storage in frozen meat, why NOT supplement it, just to be sure?