Is a graphic tablet used in drawing an anime or manga?

Use of the graphics tablet (e.g Wacom's Intuos) depends on the manga author's preference.

In Hoshino Kastura's (author of D.Gray-man) photo of her working studio, a gigantic graphics tablet that looks like a Wacom model can be seen.

(source: D.Gray-man Official Fanbook Gray Ark page 226)

In Sorachi Hideaki's (author of Gintama) photo of his working studio, there does not seem to be any computers in the photos.

(source: Gintama Gonensei Official Fanbook 2 page 190~191)

It is most likely that Anime creators use tablets since using computers is the de facto industry standard now. Sunrise Studio even use special keyboards in some situations.