So… Hades, the god of the Underworld, named his dog ‘Spot’?
Nice. 
Yes. I’ve read this elsewhere.
In this famous Greek vase Kerberos isn’t depicted as spotted, but the snakes attached to him* are.
Yahoo Image Search…&p=Herakles+Kerberos+vase+painting&oid=8396beefa22305526dab90dee70cb6ef&fr2=&fr=yfp-t-901&tt=Seneca%2C+Hercules+Furens+46+ff+%28trans.+Miller%29+%28Roman+tragedy+C1st+A.D+…&b=0&ni=288&no=11&ts=&tab=organic&sigr=12c73cms4&sigb=13v66f45e&sigi=12l76hu86&sigt=129djiefp&sign=129djiefp&.crumb=KF3D/tqJmTZ&fr=yfp-t-901
*Snakes are a common attribute of “underworld” figures. I know of no text that describes Kerberos as being covered by snakes, Medusa-like, but you can see it in depictions like this
