No. You can assign a Salesforce user either to Genesys Cloud for Salesforce or CX Cloud from Genesys and Salesforce.

You can have both the setups Genesys Cloud for Salesforce and CX Cloud from Genesys and Salesforce running together in your environment, but you cannot assign a Salesforce user to both the setups. For other limits and limitations for Service Cloud Voice, you can refer to the Salesforce documentation.