[greysome]

Are you talking about Ensure as in the shakes that come in cans and bottles? There is a ton of sugar in that and I'm not sure whether or not it can be taken with whatever antibiotic he's on. Maybe you can look at pedialyte or something else instead--I think I've heard of people giving their hammies a little pedialyte when they were unwell to help keep up hydration and some electrolytes.

I don't know about the excessive grooming but does he have access to a sand bath? I'm not sure whether it would be a good idea for an unwell hamster but am asking anyway because you said his fur is looking oily and perhaps he is grooming excessively in part because he isn't really feeling well and his face area in particular is bugging him and partly because his fur is oily. The sand should help remove excess oil.