Much depends on how severe the diabetes is, but here are a few ideas for replacements/substitutions - fruit and cheese with whole grain crackers or flatbread; pizza is okay (thin crust or whole grain crust is better); chocolate-dipped frozen bananas in place of ice cream; if bringing chocolate, hit Trader Joe's for their sugar-free chocolate almonds for the diabetic man. I usually hate sugar-free anything, but Trader Joe's chocolate almonds are really good!
Is it possible that your husband could ask the new guy about what he likes and what snacks might work for him, given his medical condition? Asking may be better than guessing, and handled well, will come across as considerate rather than nosy.