How can alchemy be used in another dimension?
It is later revealed that


   The energy source for Amestrian alchemy is human souls, just like how philosopher's stones are made and used.


Gluttony was meant to host a philosopher's stone in his body formed from the red water and humans he consumed, so


   I would say that there is vast alchemical fuel in his "stomach", or whatever you call that alternate dimension that consumed objects are transported to.


Hence, alchemy should be possible in that dimension.