Anaesthesia normally depresses laryngeal movements, making diagnosis of laryngeal paralysis challenging. The animal should be anaesthetised to the point at which the mouth can be easily opened but a laryngeal reflex is still present.
If jaw tone is such that you are afraid of being bitten during the examination, then the plane of anaesthesia is appropriate. If the GA is too deep, the patient will not have normal vocal fold movement and even a normal larynx may appear paralysed. In this case you should wait for drug redistribution allowing the patient to approach consciousness and repeat the examination.
Exposure of the larynx is more readily accomplished with thiopental or propofol than with diazepam-ketamine.