Don't know a thing about Jawfish, but my 4" horse-faced loaches can burrow just fine in gravel. Mine is pea-sized & smaller, about 3"-3.5" deep. IDK that tunnels are going to hold up with gravel, but the fish will create new tunnels as they, well, tunnel.
My cories love to tunnel and I had them in gravel at first and then switched all of my tanks to sand and they like that sooo much more than the gravel. From what I understand, sand is usually recommended first for munchkins who like to dig.