Hi Hogloopy and Baldwin Hedgehog
I’m afraid slugs are a bit of an occupational hazard with feeding hogs. In my experience, they eat just about anything, if there is moisture around. I have even seen them eating dog poo (although that probably had something to do with what the dogs ate, I imagine).
I agree, Baldwin Hedgehog, that they may not find cat biscuits so interesting, but I would urge caution about adding mealworms and sunflower hearts. Mealworms have a bad Calcium Phosphorous ratio which may cause leaching of calcium from the bones, causing Metabolic Bone Disease. This is particularly worrying when hoglets are around (i.e. now). Sunflower hearts are not quite as bad but also don’t have a particularly good ratio, so I would not introduce them to the diet either.
The following is a video about Metabolic Bone Disease. You may find the beginning distressing, but it is worth persevering so that you can understand what the problem is.