To believe that technologies like DIF and integrity streams can protect you have to believe that backups corruption can only come from block level/bit rot type disk corruption, i.e. that no possible bugs exist in Veeam, the OS (filesystem and device drivers), the data source (i.e. CBT) and that nothing environmental can impact backup data (a BSOD at an inopportune time).
In the lab I've already seen corrupt backups on ReFS due to what appears to be a Windows issue that caused the system to BSOD during the synthetic fast clone operation. Admittedly in this case the old backups seemed OK, but the chain itself was unrecoverable and I had to run active fulls.
I will admit, if you use storage with DIF level protection, or ReFS integrity streams (assuming mirror/parity storage spaces), have offsite copies of your data, and run health checks/perform compacts, that you should be very, very safe, much safer than any technology previously used to store Veeam backups, however, it's still hard to argue that running the occasional active full wouldn't offer at least some additional benefit.
It really comes down to how risk averse you are. I've spent a lot of years planning for disaster and I know that what has saved me many times is being as risk averse as possible, because that makes you take the most conservative approach. Perhaps, as time moves on, and ReFS proves itself in the field to be truly resilient to bit rot and other issues (based on support cases), I'll feel better about it, but for now, I still think the occasional active full isn't a bad idea, even if it's not "needed".