It’s reliable to use the account profile - but you’re going to have distracting information or warnings from the “stranded” account activity entries since verification will not be possible.
The Standard Services Before Provisioning rule is a rule developed by SailPoint PS that allows you to modify configuration on the source configuration. So if you want to change what OUs it’s being moved to, you can update sources & transforms instead of rules. The rule itself reads the configuration on the application source object. You can have SailPoint deploy this to your tenant through a CS tenant and they can provide the documentation.