The first parition with the Windows bootloader would be unencrypted and thus bootable, but there wouldn't be any NVMe drivers there. I believe it needs both coopoeration from UEFI and some additional support in Windows, specifically for NVMe, to unlock the other partitions. I see that most X99 boards have received this BIOS update.
I can't test as a 2nd drive as my laptop is a single NVMe only, I hope when you fix this you inform Dell what they need to do BIOS wise or they will ignore the problem. Thanks to this I have a drive that can no longer be secure erased. You need to release the PSID revert tool like other manufacturers have done so we can put out drives back into a state where we can use OPAL, sending for RMA is not a solution unnless you are going to cross ship me a drive.
While I'm still angry that I can't use main feature of my premium product (i.e. security), there is a simple check, if BitLocker is able to use hardware encryption of SSD:
run elevated msinfo32.exe and for my system (DELL XPS 9560) I see:
Device Encryption Support Reasons for failed automatic device encryption: Un-allowed DMA capable bus/device(s) detected, which is indicating that HW encryption is not possible.