Yes frozen french fries or frozen fries or potatoes can be put in the deep fryer as long as you do it safely to avoid a splash back of the cooking oil which could cause a fire.
When you place frozen fries in the deep fryer while it's hot you should lower the deep fryer basket slowly to avoid the cooking oil flashing back on you.
Or you can add the frozen french fries or frozen fries to the deep fryer first and then turn the deep fryer on and they will cook just fine without flash back the cooking oil
There was a house fire once where a person was using a turkey fryer outdoors and dropped a frozen turkey directly into the hot oil which then flashed back and caused the guy to get burned and burned the house.
But as long as you put the frozen fries in slowly and safely then it's okay but I would place the frozen fries into the deep fryer and then turn the deep fryer on so that you don't have the cold fries making immediate contact with the hot oil