There’s more than one connection, actually. For one thing, both are American classics and legends of the genre. Both are also based on true stories. But if we get a little more specific with it, certain events dramatized in one of the films, the one starring the Fouke Monster, actually happened in both real-life incidents. (Allegedly. I mean, we can’t prove that things played out the way the eyewitnesses described.)
Remember that scene towards the end of the movie where the Fouke Monster attacks—ahem, “attacks”—the farmhouse. After the people inside get it good and riled, one of the guys goes to the toilet. The Fouke Monster reaches in through the window to grab him. It serves as a fantastic climax to the action, but it is, according to the people who lived it, exactly what took place in reality.
During the Kelly-Hopkinsville “attack” (which we know inspired the movies GREMLINS and CRITTERS most directly, although it also played a part in E.T. and POLTERGEIST, too) there is a parallel incident wherein one of the witnesses, upon stepping out onto the front porch of the house to have a look, has a little clawed hand reach down from the rooftop to try to grab him. Both occurrences, both the one in Arkansas and the one in Kentucky, elicited the same reaction from the witnesses. I’m betting it would get the same kind of reaction from you, too.