I used to worry about this a lot being the medic/EMT on vessels where we were far from support, used a lot of hydraulics (cranes, winches, etc.), and all the equipment was subjected to lots of corrosion (i.e., we popped lines regularly).
I don't so much in normal situation, and especially with something like a log splitter. Unlike compressed air systems, there is almost no stored energy in a hydraulic system (because the fluid is more or less incompressible - at least at the pressures we're dealing with). So, as stated above, you pretty much need your hand covering the break point to received a hydraulic injection, and the motors/pumps on a log splitter don't deliver enough drive to continue to push enough force to be of significant worry. Now if it were a 100HP motor driving a big swash plate pump, it might be able to continue to deliver a high pressure stream that you would need to be cautious of.