There are lots of veggies that are very low in sugar that would probably make a fine treat for a diabetic piggy. But you need to consult with your vet on that. My
guess would be that things like certain lettuces, cilantro, endive which are quite low in sugar will be fine for your piggy, in moderation. But I am
not an expert on diabetic pigs, so
please don't feed your piggy anything else without checking with the vet. I'm just writing to reassure you that your piggy will almost certainly not be relegated to pellets and hay only.
Hang in there, but don't give "treats" without knowing what you're doing.