The simple answer would be no.
tinyG provides On/Off and direction control signalling for a spindle as well as a continuous, single phase PWM stream whose duty cycle is related to the S command via a programmable linearization of a range of speeds.
G code commands M3, M4 and M5 as well as S are the controlling parameters.
It might depend on what you are really trying to implement.
If you are manually coding a Gcode stream to implement some sort of robotic movement, you could code complex XYZ motion and manually edit in continuous rotation on a rotary axis (A,B or C), I suppose