For reference, here's picks of Smeargle, Snoopy (another cartoon beagle) and an actual beagle.
for the record, I always just saw smeargle as smeargle, never really clicked what he was meant to be other than a vaguely animalistic artist. But I think adding in Snoopy helps. Between the two. You can see the tail tip, the ears, the eye markings, the head shape, feet shape, and mouth placement.
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This might seem arbitrary, but snoopy was first introduced to Japan in 1968, and Ken Sugimori was born in 1966. There's a hotel dedicated to snoopy in Japan, and the only satellite snoopy museum is the one in Tokyo. It's absolutely possible snoopy is an influence on Smeargle.