Yes, however there are several grades and brands of carbide and they all react differently to the cryo treatment. Some show no significant increase while others show dramatic increase. We'll be happy to do test samples on carbide.
Yes, the process will still make the underlying material tougher and stronger. Coatings wear off. Cryogenics doesn't. The process keeps working for the life of the tool rather than ceasing to be effective after the surface is worn or otherwise damaged.