Here is your clarification from the GCR 9.3.26 this is section 4.
4. Rotary Molded Cell
The use of rotary molded fuel cells not having a bladder, or not contained in a metal can, is allowable in those cars that do not require the use of a fuel cell, but where they are an allowed option.

Fuel cells were an option in IT last time I read the rules. This should clear up the confusion.