The IOM6 units are just dumb expanders, they do not support zoning etc splitting of the shelf.
They just give direct access to all drives and thats it.
On paper you can split it by just connecting both and making sure you dont use the same drive for both servers.
(Would expect you to need the interposers if this is sata drives)
Have not done this myself but ive seen it done in multiple setups.
The cleaner approach imo would be a virtual truenas etc file server that runs on the host needing lowest latency and shares to the rest.