Can I host Unlimited Domains in a Cloud Server ?

Yes. You have complete root access like a dedicated server. You also have cPanel / WHM installed FREE in Centos based cloud servers. This enables you to host unlimited domains in a cloud server. However, make sure that you have enough CPU, RAM, Disk Space to run so many domains you wish to host. Ideally to host multiple domains, it is better to start with Cloud Servers with min 4 GB RAM / 4 vCPU