The datasheet is painfully thin when it comes to electrical specification or system hardware. Is there any detail available regarding the voltage tolerance of the SPI/UART bus? Is it possible to interface directly with a 5V system or will it be necessary to use a level shifter?
You will need to use a level translator. Given all of the units run off 3.6V because they are all designed around lithium ion voltages nothing it rated to 5V, also the input high for a given SPI/I2C device would need more than the maximum possible 3.6V the unit could go up to even if it wanted to.