Hey Tommy,
on the four-axis buildbotics-derived ➪ Onefinity Original X-35/X-50/PRO Series Controller you don’t have a fifth axis driver for free use, but you can nonetheless attach a rotary axis, either by running both Y axes on one single driver (instead of running them by using two drivers as is the default), and to assign the slave Y internal stepper driver to motor A, or by simply not using one axis and to reassign this axis driver to motor A. In the latter case you would e.g. not use Y axis and travel with X and Z over rotating A axis.
How this has been successfully done on the buildbotics-derived Onefinity Controller is described here.
One advantage of the buildbotics-derived Onefinity Controller of the Original/X-50/PRO Series is that the stepper drivers are already included so you can connect bipolar steppers as found on rotary axes directly (unlike the Masso G3 which requires an external stepper driver for each stepper motor, or stepper motors with integrated drivers as on Elite machines.)