You may have 2 deadman switches under your pedal. Newar easi's are like this, one is for lift other is for travel.

I think you need to be a bit more specific as to what you want to do, do you want the deadman pedal to de-energize all systems? If yeah then I am sure is doable, just look at the wiring diagram and see where the deadman switch is attached to, and wire your directional controls (steering, driving). I've never seen a forklift that can move without the deadman pedal depressed, but I have seen forklifts able to move hydraulics without deadman pedal depressed I guess it depends on the model. I am not familiar with this specific orderpicker but we have orderpickers here too.

On the new model trucks comming out now generally the deadman switch is wired so that it has to activate a line (power) contactor to energize the system before anything will work.

On the older trucks they weren't wired in this way and the hydraulics would work even if you were off the truck.

It has become apparent to me they have done this as a safety measure to keep any system from working while the operator is not on the truck.

So to answer your question about making the hydraulics work without depressing the deadman? i'm sure its possible but would you want to bypass a "safety feature" on the truck?