Dell uses trusted platform modules (TPM). It's a separate chipset than the BMC chipset.
For a mostly open source solution, not only would you need open source BMC firmware, you must have an open source UEFI/BIOS/boot firmware like CoreBoot, LinuxBoot, Oreboot, Uboot, etc.
https://www.dell.com/en-us/blog/hardware-root-trust/