At MedAustron, a synchrotron-based cancer therapy center located in Austria, Optical Emission Spectroscopy (OES) has proven to be an effective technique for monitoring ion source stability, offering a non-invasive alternative to traditional beam diagnostic devices such as Faraday Cups (FCs). Measurements were performed at the MedAustron injector on one of the three identical Electron Cyclotron Resonance Ion Sources (ECRIS), used for non-clinical research. For carbon ion beams, a clear correlation was observed between intensity variations in emission lines of neutral and ionized atoms in the visible range and extracted current instabilities measured on the FC. In this work, we present a study on the correlation between OES and extracted current measurements for proton and helium ion beams as a function of source parameters. Additionally, plasma characterization via OES was carried out to determine plasma parameters such as electron density and temperature via the line ratio method using the YACORA Collisional Radiative (CR) model. The results of this measurement campaign show that the applied methodology is a valid tool for monitoring source stability in parallel with clinical treatment, enabling faster detection of source instabilities and ultimately reducing downtime and speeding up low intensity investigations.