That could very well happen.
The voltage and the current from a test meter are both insignificant.
The reason why low voltage isn't dangerous usually, is because the skin is a damn good insulator requiring voltage above 100v to break (one of the argument invoked by countries using 100volts, whereas the rest is 220v).
The Darwin Award example did stick needle-like pointy ends of the probe *through* the skin. The skin's high insulation/resistance wasn't there any more to shield against "insignificant voltage". The serum of the blood isn't distilled water but is filled with electrolyte. Quite conducting mix. It also runs through the hearth. The rest of the fuilds inside a body are all rich with electrolytes too. That means that the *inside* of a body can conduct electricity quite well, and the hearth can easily get in its path (specially if you put each electrode pole at opposite side).
(one of the reason why it's not a bright idea to swim during a storm. the inside of your body is a *better* conductor that the water around you in the swimming pool, the skin is the only thing in the way blocking the electricity).
The actual delta-V needed for a muscle cell or a nerve to react is quite low (a few dozens of mili-volts are needed to rise above the threshold and cause contraction or impulse propagation). So with the skin barrier removed, it's quite likely that the remaining salty fuilds (mostly blood, but also extra-cellular fluids) can carry enough to cause a jolt to the hearth, enough to disrupt the normal rhythm.