Hi Mathieu
I don't know the specific scheduler product you mention but in general what I've seen at customer side when an external scheduler is involved is the following. If your strategy is to schedule in as much jobs as possible in the external scheduler:
If you can schedule it in using the external scheduler, you do that and that's normally possible for 90% of all jobs or something like that.
Some jobs potentially cannot be scheduled in through an external scheduler because they might be event based or generate temporary variants and in those cases you can't always managed that through that external scheduler. Those jobs then typically remain inside SAP's job scheduler.
Best regards
Tom