The PocketWizard IVs are manual-only triggers, and ISO-compatible, so you should at least be able to fire an i40 in sync with the camera shutter. Whether the group/zone settings will work is unknown. And you won't have any remote control over the flash settings, such as zoom or power.
However, if you're fine with manual-only, you don't have to get an i40. The i40's virtue is that it can perform TTL (and HSS) on a Fuji X hotshoe. But if you just want to fire a flash manually off-camera, there are a number of more powerful, cheaper, manual-only options. A LumoPro LP180 at the high-reliability end of the spectrum, down to the super-cheapies like the Yongnuo YN-560IV or Godox TT600.
Many of today's manual-only flashes also have remote power control built in, if you use a same-brand transmitter on-camera (e.g., LP180R+Phottix Odin; YN-560IV+YN-560-TX; TT600+X1). But since you already have the Plus IVs, that may be a moot point.