Both etherscan & sourcify.dev are supported by the @nomicfoundation/hardhat-verify package, but ignition verify doesn't allow you to select which verifier to use as it defaults to Etherscan

The verifyEtherscanContract function at https://github.com/NomicFoundation/hardhat-ignition/blob/2ece9520446adc495f9ad9c87ef5605e39fb62f5/packages/hardhat-plugin/src/utils/verifyEtherscanContract.ts#L4

Is used by the verify task at: https://github.com/NomicFoundation/hardhat-ignition/blob/2ece9520446adc495f9ad9c87ef5605e39fb62f5/packages/hardhat-plugin/src/index.ts#L532

The sourcify module for hardhat-verify is at: https://github.com/NomicFoundation/hardhat/blob/main/packages/hardhat-verify/src/sourcify.ts