Well for one thing, the Job runs inside the IDM process space. If the IDM process goes down, the Job is down. The IDM process runs inside the ndsd process space. If ndsd goes done, you lose IDM and you lose Jobs.
I would recommend both. Health job can do more things, and have more insight into the driver health.
The script is useful to catch driver stoppage from outside the IDM system.
You should do both.