For the Dell r730xd, the H730 controller would be the onboard controller and any disk being plugged in would need to go through this controller.
I didn't have time to test if just running SD and no scratch. I also didn't have a spare SAS drive to swap with. Based on all the logs and data I've collected, on the older firmware 25.2.2.0004 probably would have not hung/crashed if using all SAS disks connected while in HBA, however HBA mode was still noticeably slower. VSAN observer in RAID0 would show drives maxing between 350-400 IOPS, where in HBA, 275-300 was max for IOPS in addition to controller hangs and all the other bad stuff. Other benchmarking that I did between RAID0 and HBA also showed that HBA was 20-25% slower on this older firmware.
The original firmware 25.2.1.0037 wouldn't even detect my SAS storage drives in HBA so I did very little testing on this.