Can deep frying oil be too hot?
Yes, certainly. Deep frying only works well in a very narrow temperature range. The optimal temperature is different for every food, but it's in the 180 to 210 Celsius range. 

The needed temperature is determined by the starch type and the amount of wetness on the outside, and is chosen such that it crisps immediately (not allowing the inside to get soggy with oil) without burning immediately. The inside doneness is not controlled by changing the temperature. If you get underdone or overdone insides at the correct frying temperature, you need to change some other variable, such as the thickness of the food, the degree of parcooking, or the food temperature at the moment it hits the pan. 

Because a good result is so dependent on temperature, I can strongly suggest both the use of an oil thermometer (a barbeque probe does it too, if it's rated for the temperature) and controlling the initial temeprature of the food (room temp, out of the fridge, or frozen). A good recipe will tell you the proper parameters for both.