20/240 Outlet split to 2 16/120 PDUs
L6-20 outlets do not carry a neutral, just two hots and ground and provides 240 volts only. As such, you cannot safely get 120 volts out of it without using a step-down transformer.

Using ground as neutral is not safe and is not allowed by the electrical code.

If you had a 240/120 volt outlet such as a 14-20, then you could safely make a splitter to two L5-20 using one hot and the neutral to each (as well as ground, of course).