Slowpoke's at least got a partial resemblance to a hippo, and is water type. Maybe it's not a dead-on hippo, but I'd say it fits the bill.
As for jackals, I'd say they probably pose a similar problem to other canines like coyotes or dingoes; they can pretty easily get lost in the shuffle with all the other canine pokémon that look like feral/wild canines. Would you say manectric's a wolf? Coyote? German shepherd? Maned wolf? Apart from purebred dogs, most canines look pretty similar, to the point that it can be hard to single out one of them for a pokémon inspiration. I guess possible distinction could be made by invoking cultural significance (like how zoroark doesn't look particularly foxlike, but it's probably safe to call it a fox pokémon because its design has kitsune references), which in the jackal's case, Anubis would probably be the clearest choice (though apparently the golden "jackal" Anubis's image was modelled after isn't actually a jackal, so not even that?). I guess there's still the chance to make one that's an allusion to some lesser known African folklore or something similar (which would be fine by me, Pokémon could use more Africa), but canine pokémon are still common to a point that it would need a lot to stand out (fennekin was actually pretty original, but it still came off a bit of a dead horse at first, being the third fire type fox pokémon, with there already being two of them from the get go).
