If you use application-aware processing (and it is possible depending on the workload) then it will be an online backup and you will get an application-aware backup which is preferred to have consistency for your data. If AAIP cannot be used, you can go in the advanced backup settings - hyper-v and choose Enable Hyper-V guest quiescence. In this case, the following will happen:
* If a VM meets all requirements for online backup, Veeam Backup & Replication will use the online backup method.
* If a VM does not meet requirements for online backup, Veeam Backup & Replication will use the offline backup method.
So basically, even if you choose Hyper-V guest quiescence, you might be able to have an online backup, but it could be an offline backup (meaning the VM will go into a suspended state for a very short time)
Last thing, if you don't want the VM to become suspended, you can select Take crash consistent backup instead of suspending VM which means we will take a crash consistent backup and not suspend the VM.
Hope it helps