I used to feed my nems just mysis/brine a while back, and they grew/survived.
Now they get one silverside a week, and have much better color.
You can actually see tips get brighter after feeding.
I do agree that clowns do help in grooming/feeding nems.
That's obvious to me as I see clowns feed the nem b4 eating for themselves.
However, I've seen many nems get beat to death by clowns that are just too big for that nem, and I think that's the case here.
That's why I suggest keeping seperated for now, let that nem heal.