TrueNAS Scale build (Inspur 5280M6): U.2 NVMe passthrough and general hardware check

Hey r/TrueNAS,

I’m currently spec'ing out a centralized storage node for a 4-node compute cluster (mostly running simulation workloads). I’m planning to use an Inspur NF5280M6 (2U) bare-metal server to run TrueNAS Scale, but I want to run this parts list by you guys first before pulling the trigger, especially regarding the NVMe backplane wiring.

Here is the proposed BOM:

• Chassis: Inspur NF5280M6 (12x 3.5" front bays + 4x 3.5" rear bays)
• CPU: 2x Intel Xeon Silver 4310
• RAM: 256GB (8x 32GB DDR4)
• Boot Drive: 2x 480G SSDs (Internal boot drive module)
• Fast Pool (Flash): 4x 3.84TB NVMe U.2 SSDs (Crucial point - see question below)
• Bulk Storage: 8x 10TB SAS HDDs
• Controller: HBA Card IT Mode
• Networking: Mellanox ConnectX-5 MCX556A-ECAT Dual-Port
• PSU: Dual Redundant Power Supplies

My main concerns:

1. NVMe U.2 Passthrough via SlimSAS/Slimline: For the 4x U.2 drives in the front backplane, the vendor claims they are "PCIe direct passthrough." For those familiar with Inspur servers (or modern 2U chassis in general), can I confirm that connecting the backplane via Slimline cables directly to the motherboard will present the U.2 drives directly to TrueNAS/Linux without any abstraction? I absolutely need ZFS to have direct, raw access to those NVMe drives for maximum IOPS.
2. HBA for SAS: I’ve specified an IT-mode HBA for the 8x 10TB SAS drives. Is there anything specific about the Inspur SAS backplanes I should watch out for when passing them through a standard HBA?

The goal is to use the 4x U.2 drives as a dedicated high-speed pool for simulation scratch data, and the 8x SAS drives in RAID-Z2 for cold archiving, all served over a 40G network.

Any feedback or "gotchas" before I finalize this PO would be greatly appreciated!