Danger of high voltage in electroadhesion
This is a 'best guess' answer based on lots of general experience but not specifically with shocking HP plotters. (I've used them long ago but they did not shock me).

The energy delivered and the current capability are what (probably) matters. In a static adhesion system with good insulation you can use a series resistor that limits supply fed current to whatever level suits.   

The energy delivered short term depends on the capacitance of the electrode structure on the load side of the protective series resistor. This obviously depends on electrode areas, inter-electrode separation, dielectric constant of the insulating layer and Murphy. At an off the cuff non calculated guesstimate capacitance figures in the 10-1000 pF range.
At 1 nF and 5000V the energy (0.5 x C x V^2) would be about 10 milliJoule = about 10 gram centimetre of potential energy. I'd expect that be enough to be felt quite well as it's delivered rapidly so the power is high for a very brief period. As the period is very small, even a large short period current will not be "cardiac dangerous" and 10 mJ should not otherwise be a threat.

Data point: Static charge accumulated on a human body on a suitably enthusiastic carpet can convey an unpleasant shock but otherwise unimportant to both parties if contact is made with another person.