Be careful about the maximum voltage you apply at the control inputs to the ESC. If the ESC specifications don't say that it is 5V tolerant then it NOT safe to assume that it is and you could damage it by using a 5V square wave.
The reason is that there are internal protection diodes on the input pins on almost all semiconductor ICs, going from the signal line to both supply rails. The diodes are there to protect the device against low energy transients (eg ringing on signal edges) by clipping any voltage on the input that goes above or below the device supply (eg 3.6V or 0V) to a diode forward voltage drop (0.7V) above or below the supply rails (eg total of 4.3V or -0.7V) in order to prevent malfunction, internal latch up or damage to the internals of the device.
These kind of transients are normally do not persist for very long and so protection diodes are not usually designed to handle large amounts of energy. If you directly feed an input on a 3.6V device with a 5V signal the protection diode will try and source as much current as it can from the driving signal and try and to pull it down to 4.2V. This can be many 10s of mA of current, which can potentially damage the device driving the signal as well as cause the internal protection diode to dissipate more energy than it is designed to and eventually burn out, which can take the device out with it.
These kind of faults may not occur immediately, but may take a while to appear as the continual exceeding of the limits of the devices can eventually cause them to randomly fail months down the track.
Some low voltage devices are designed to be 5V tolerant and their data sheets will will tell you it is. Unless a low voltage device is guaranteed to be 5V tolerant, you should consider at least a series current limiting resistor or some kind of voltage level translation device or divider circuit between all 5V devices driving devices on lower voltage power supplies.
So the moral of the story when dealing with devices with mixed supply voltages is to always make sure the data sheet for the lower voltage device say that it can handle what the higher voltage devices dish out.