Is there any way to get the list of all attached vCAC host to vCenter Orchestrator in the VCO workflow?
Yes:
vcacHosts = Server.findAllForType("VCACCAFE:VCACHost");
Yes:
vcacHosts = Server.findAllForType("VCACCAFE:VCACHost");
Or switch the type to vCAC:VCACHost if you need to get the IaaS hosts.