does anyone have any experience or opinions around the storage of the below items using a fibre channel SAN and mounting them remotely so Splunk can access them as it otherwise normally would?
When you use the terms "mounting" and "remotely" are you actually meaning sharing your knowledge objects via a NAS mount(ie: using NFS). If so , then THIS LINK has some good info on such an architectural pattern for search head pooling.
As far as presenting SAN(block level) based storage over fibre channel to the OS, so it appears as local disk (vs explicit remote mounting)...then installation and treatment of the etc/apps & etc/users directories is no different than to using a local physical disk. Only thing I can think of really is that if using virtualisation, you may want to consider RDM for direct LUN access vs VMFS.