Freeze/thaw in Proxmox does the same as VMware Tools Quiescing during snapshot, which also calls VSS but is a fallback option in Veeam Backup.
AAP in Veeam is much more precise and open the way to transaction log backups and granular applications...
Freeze/thaw via qemu agent will never be the same as Application Aware in Veeam for VMware/HyperV. It also frequently generate SQLWriter/VDI errors on Windows VM with SQL Server.