Certainly. Project Alchemy and ZETH are both decentralized exchanges meant to allow easy exchange between ETH and ZEC, but neither of them is an altcoin meant to combine both currencies in one blockchain. What this essentially amounts to is: you can have privacy in your transactions, or you can have smart contracts, and it's easier to switch between the two...but you can't have both simultaneously.

Hawk, OTOH, would be an altcoin that actually allows you to have private smart contracts. Theoretically, if ETH incorporates SNARKs into its protocol, it could have private smart contracts as well...but I don't know how far down the road that is. Besides, the Hawk protocol also has mechanisms to make private smart contracts less cumbersome than they would be in ETH.