At this moment, the Scheduler doesn't support loading additional resources during scrolling. All resources need to be loaded in advance using .resources array.
However:
1. The row headers are rendered progressively so loading a large number of resources scales relatively well.
2. If your resources are organized in a tree hierarchy you can load the node children on demand - http://doc.daypilot.org/scheduler/dynamic-resource-tree-loading/
The events can be loaded on-demand (during scrolling).
See the following doc page for more details:
http://doc.daypilot.org/scheduler/dynamic-event-loading/
See also the following tutorial (it includes sample PHP project):
http://code.daypilot.org/85715/html5-scheduler-with-dynamic-event-loading