In Young Dracula a "Hellhound" appears to be a type of wolf with grey fur. Zoltan is the only hellhound who appears in the series and he is a taxidermy victim (he's stuffed with sawdust). Hellhounds may be able to talk as this is an ability which Zoltan possesses.
In "Dad's Back" Zoltan mentions how he was once part of a pack of hellhounds who tore apart and ate Renfield Senior. Given this information it seems likely that hellhounds also have a taste for human meat.