In one of the episodes of the new Ducktales series, "The Depths of Cousin Fethry!", Huey, Dewey and Louie meet their Uncle Fethry and have an undersea adventure with him. Fethry also has a small part in the hourlong episode "Moonvasion!". He's actually paired up with Gladstone Gander, who had previously appeared in the episode "The House of the Lucky Gander!". (Though Gladstone is dressed in green instead of his usual purple.) And the hour-and-a-half-long series finale "The Last Adventure!" opens with a birthday party for Webby. Fethry is one of the guests and once again he's paired up with Gladstone Gander. (And one of the other guests is Drake Mallard.)

Is this the first time Fethry Duck has been animated?

As far as I know, yes. The show has a few other characters who have never been animated before (ie. Bombie, Rockerduck, and of course, Della).

It's interesting how many characters from over the course of Disney history have put in appearances in the new Ducktales series. In addition to the characters mentioned above, there have been appearances by:

Goofy (dressed as he was in Goof Troop)
Jose Carioca and Panchito Pistoles
Ludwig Von Drake ("Ludwig Von Drake? You were ancient in the Sixties! How can you still be alive?")
April, May and June (though in a very weird way)
The Phantom Blot
Chip, Dale, Monterey Jack and Gadget Hackenwrench ("I think you have a rodent problem.")
Don Karnage
Bonkers D. Bobcat
Steelbeak

And the hourlong episode "Let's Get Dangerous!" included a slew of Darkwing Duck characters: Gosalyn, Taurus Bulba, Megavolt, Quackerjack (and Mr. Banana Brain), Bushroot and Liquidator.

(Noticably absent was "the world's most famous mouse", unless you count "Mickey Melon".)