Actually researches have shown that lesions or damages in any cortical and subcortical areas can cause stuttering. For example, lesions in the pons ( https://www.sciencedirect.com/science/article/pii/S0278262603001064) and lesion in the cerebellum (https://www.sciencedirect.com/science/article/pii/S0094730X10000239) can cause stuttering. So yes, a tumor in the cerebellum may cause stuttering.