Yes it can.
The quickest way is to teach it a TM.
Prinplup learns Hydro Pump at level 51.
Prinplup learns the the moves Bide, Bubblebeam, Fury Attack, Brine at level, Wirlpool, Mist, Drill Peck, Hydro Pump. Also don't let your Prinplup evolve until it learns hydro cannon because it's the strongest move empoleon and prinplup can learn and prinplup learns the move at a lower level than empoleon does.
No, Dragonite cannot learn Hydro Pump.
Floatzel cannot learn Hydro Pump.
Quagsire cannot learn Hydro Pump.
Azumarill learn Hydro Pump at level 57.
At level 40, Kingdra is suposed to learn Hydro Pump.
Swampert does not learn Hydro Pump.
Pokemon learn moves at there time. Empoleon learns Hydro Pump at level 59 because it can!! Because every time you evolve3 a Pokemon its stats get better but the learning of a new move takes longer. So, for example, if you had stopped the evolution of prinplup to empoleon you could have learned hydro pump at lvl 51.
No, Floatzel does not, and cannot learn Hydro Pump without the use of hacking.
Floatzel cannot learn Hydro Pump without the use of hacking.
It learns Hydro Pump at level 48.