To the first, nothing really. Combee honey is almost identical to actual honeybee honey; the only difference is that pokémon prefer the former due to its stronger scent. (Some people likewise prefer it, although honeybee honey is a little sweeter.) Thus, it’s perfectly safe to use combee honey for mead, provided the combee willingly gives it to you.
For your second question, no. Alcohol is actually poisonous to most species of pokémon. For the ones that can drink it without literally dying, it would still be unwise to give them alcohol. After all, would you really want something that’s capable of wielding the very elements of nature itself to do so drunk?
The Pokédex According to Bill 