Hydraulic fluid is oil, brake fluid is propylene glycol, totally different stuff.
You can hook a LeverLock into the rear brake line as easy as anything else. I doubt that a non-DOT non-SAE valve would pass any kind of safety inspection.
The best thing about the 'Lock is that you set it, then push the brake ...a one-way valve lets the fluid through to apply the brakes, then holds them on until you release them. Much easier operation.