He meets the most obvious criteria to be one, but IIRC he's said he doesn't consider himself to be one and he just uses the doggo to have something interesting on the screen while he talks, so I guess we should take his word for it. The doggo model itself is a stock character that comes with one of the vtuber software packages; I've seen others on Twitch using the same model. He does have his own customized versions of it, though, like the guntified version he used last night, or the one in Gura's shark hoodie he used tonight.
But I guess if we want the final word, we could ask him ourselves.
@Flamenco ?