My experience, I have had this combo in a 75 gallon with absolutely no problems. Dusky Jawfish are pretty cryptic and stay tight to their holes, even closing the top at night. YWG generally will find a overhang, or comfort area and tend to stick to that location. With all likelyhood they will rarely be face to face, assuming they are of similar sizes and stay that way, I would not be worried at all about predation.