I've got one or two he could certainly know. First up is obviously Wilhuff Mulciber! While Wilhuff is sort of bonkers he's still one of the top-ranked Death Eaters, having been around since Voldie was 'Tom Riddle.' He's an expert in dark magical objects and despises muggleborns and muggles, as he blames them for the downfall of the Mulciber name. Something here?
Next up is Anton Dolohov! Current Death Eater and possibly future defector. He's been with the DEs for a while now because of his father, who may know Jasper. Either way, Anton treats him with respect.
Then there is Sirius and Hamish. Don't think there is much connection there. Jasper might know Sirius' family, as they are also a bunch of purist assholes, but who knows!