Hey Hey Bman,
Unfortunately, I don't know of any. There doesn't appear to be any Piano Slim (blues) videos on YouTube, but I think there's a chance some might exist. If I'm not mistaken, the recently deleted James Crutchfield video "Boogaloo City Blues" (actually "Bogalusa Blues") and the R.L. Burnside video "Poor Black Mattie", among others, were recorded in the Netherlands by Swingmaster Records in the early 1980s. Since Slim also recorded for Swingmaster at that time, it seems possible they would have also videotaped him.
Great website, Bman – you've really got it covered – even a bio of Bat The Hummingbird … very cool.