well it depends what you want to do. do you want to install dp agent on all virtual server to do backup of them like they would be physical servers or do you want to backup the virtual servers with image backup (vStorage API).
If you want to do image based backup (the whole contet with configuration, container and so one) the you need one online extension license for each physical hypervisor host. If you want to do GRE from those Backups, you need one gre license each host
About the application integration, this means if you want to backup for example Exchange Database, or SQL Server DB online. then you need one of those licenses for each server with one of those Applications. If you just want to do a traditional file level backup, no additional licenses are required as bob said