It supports it, but ZFS itself is operating on the host CPU, not the RAID controller. Additionally, ZFS prefers that the RAID controller is disabled/defeated and operating in JBOD mode where disks are passed-thru to the OS without any caching.

Not just caching. The problem is that non-JBOD HBAs also swallow error codes and mask retries, meaning ZFS is potentially unaware of some read errors and is not in control of the latency as the controller firmware has its own timeouts and retry counters. Moreover, most will not pass through SMART or else fake it.