As far as I can tell, Reflect's interface itself doesn't have a way to configure this. But either of the options you describe will work. Also note that you can have Reflect generate a batch file, not just a PS or VBS file. You don't get as many options that way (and you have to create separate batch files for separate backup types, i.e. Full/Diff/Inc), but if you're more comfortable with batch files and it does what you need, then it may be the best option for you -- or it might at least give you a baseline for you to expand on.
If on the other hand you make some other batch file the "master" script that just calls Reflect, you're correct that managing your schedule within Reflect would be more difficult, if not impossible. Reflect only shows scheduled tasks that it creates, and I don't think the ones it creates are editable by users within Task Scheduler, at least not without jumping through hoops. And if memory serves, some people who have jumped through those hoops have found that while the tasks still work, they're no longer displayed within Reflect.
If you can't get the batch file option to work, I would be willing to help with the PowerShell piece. You'd use the Start-Process cmdlet to invoke an external batch file, and as long as your batch file returns a non-zero exit code when it encounters an error, you'd be able to capture that within PowerShell and then have a simple If/Else statement to handle whether to proceed with the rest of the Reflect-generated script after that batch file completes. In fact there's even an example of this within the PowerShell script that Reflect generates. But here's basically what you could write:
$MyBatchFile = Start-Process -FilePath C:\MyScript.bat -ArgumentList "-arg1 value1 -arg2 value2" -PassThru -Wait
if ($MyBatchFile.exitcode -ne 0)
Write-Output "Batch file failed, skipping backup"
In English, the above means, "Call MyScript.bat using these parameters and values, and wait for the batch file to complete before proceeding with the rest of the PowerShell script. (The PassThru argument causes the process execution to return an object with some information about the execution, which is important because that's what you're capturing in the $MyBatchFile variable that you'll be checking next.) When the process completes, if the exit code of that process execution is not equal to 0 (success), then exit the PowerShell script with exit code 1, i.e. Error." If your batch file returns multiple possible error codes and you want to take different actions based on that, you can use something called a switch loop to efficiently express that.
Macrium is working on implementing their own scheduling engine in order to get away from Windows Task Scheduler in order to deal with some strange issues it seems to have, which aren't technically Macrium's fault but which impact Reflect's operation since Reflect currently relies on WTS. No ETA on that yet though.