Slurm is endian and word-size agnostic; there's nothing about the POWER9 platform that would be insurmountable for it to run on. There are occasionally some teething issues with NUMA layout and other Linux kernel differences on newer platforms, but this tends to affect everyone, and get resolved quickly.

My understanding is that Spectrum (formerly Platform) LSF was included as part of their proposal.

It could be---I really don't know. SLURM ran the BG/Q very successfully, which was PowerPC.