Now, in the 4th edition, Xenology was published. In this book, the Hrud were depicted as a creation of the Old Ones, poisonous, parasitic scavengers that generate a time-warping entropic field and looked like weird monsters (OP's picture). Their anatomical and cultural description matched most of their previous depictions (a tail, four fingers, cloaks and rags)
Since then, in the 40k RPG (in Dark Heresy and Rogue Trader, mainly) the Hruds have been mentioned a few times. Their entropic field and poison-based equipment were mentioned, suggesting that Xenology has been acknowledged by other authors, but they haven't been described physically.
In the 6th ed rulebook, there's a new illustration of an unknown xenos, extremely similar to the 3rd ed Hrud illustration. We don't know whether it's supposed to be a Hrud, a Skaven, or something else. But it's obviously different from the 4thed/5th ed Xenology Hrud: it could be a Skaven, but seems to lack fur, has a greenish skin, and doesn't seem to have a snout.
To make matters worse, in the 1st edition rulebook, there's a drawing by Jes Goodwin of an unidentified xenos, with a gasmask, a large coat, and a jezzail. But it has six digits on each hand.
So, basically, there are many similar species of xenos that all seem to roughly match the illustration of the 3rd ed rulebook. Hruds could either be green-skinned little critters, Space Skaven, the monsters described in Xenology, or the unidentified Xenos from the 1st edition.
GW's official stance is extremely vague, but the recently-released material points towards their Xenology description.