At the moment, this isn’t possible. However, with some of the upcoming Client API changes, you’ll be able to access the CreativeTab of a particular ItemType. Note that the creative tab information is still accessible server-side, it’s just that it will be added to the API along with client-only features.
This will most likely be added along with CreativeTab support in the API. However, this will unfortunately only be accessible on the client side, as the server doesn’t have the item icons available.