The QVWs may fail reading data from the QVD's if the Generator starts updating them at the same time. The only consequence is that the top-level QVW reload task will fail and the previously published version of the affected QVW will stay put. QDS throws away all (temporary) documents that couldn't be reloaded succesfully.
Another result may be that - as you said yourself - QVDs end up being corrupted. This means all reload processes may start to fail because the Generator won't be able to do a decent Incremental Load. And at the same time, the four top-level QVW jobs will fail because they cannot read a corrupt QVD. They won't run anyway if their tasks are triggered by a succesful Generator reload.
Try to spread these tasks in order to avoid writing and reading the same QVD at the same time.