Pets, On-hit, On-ability and other effects

Solution 1:

Pets do not inherit item effects (either passive or active). The only item effects that would affect pets are such effects like Banner of Command, Runic Bulwark (and its component item, Aegis of the Legion), and the Captain boot enchant.

Specifically, Malzahar's pets scale strictly off of his stats and are not affected by anything other than these items, meaning that also will not proc Red Buff. Malzahar's pets also do not inherit life steal.

P.S. If you have questions about other items, look for the keyword "minion". Unless specified in such a way, most items will not affect pets.

Solution 2:

Although voidlings will NOT proc on-hit effects, they WILL do physical damage with their attacks. Now, the description of the Black Cleaver says: "Dealing physical damage to an enemy champion reduces their armor by 6.25% for 4 seconds" In theory, voidlings should reduce the armor of enemy champions because their damage is listed as Malzahar's damage. Try it, and find out for yourself ;)