I finally managed to run Haiku on real HiFive Unmatched hardware.
Post on Haiku forum: https://discuss.haiku-os.org/t/my-progress-on-real-risc-v-hardware/10963.
Note that some information (CPU frequency, copyright year) in about window is currently wrong.
Patchset and test USB image is available here: GitHub - X547/Haiku-riscv: Haiku port to RISC-V architecture. SD card is not supported, use USB or NVMe.