It's not worth it.
The Dragon's Den Dratini comes at level 15. To get it to level 55, you'll need 203750 experience. It'll still level up slowly after it evolves, so you'll have to continue grinding it throughout the game. There is no good reason to put that much experience into an okay Pokemon when you can put in about half as much experience and get one of the best Pokemon in the game. That Pokemon is Webster's Kenya. Even though Fearow's stats suck, Kenya gains experience exactly 15/8 as quickly as Dratini. Experience is proportional to level cubed, so the same amount of experience can raise Dratini to level 55 or Kenya to level 68. That's more than enough to make up for the difference in stats. On top of all of that, Fearow is normal type, so it gets STAB from return, which is far stronger than any of Dragonite's STAB attacks.
Besides, grinding a Dragonite gives you a ground Dragonite. Wouldn't that only worsen its ice weakness?