I do believe that set bonus's only effect you, and not your minions. Now if an IO has a proc on it then THAT can be set off by your minions, but set bonus's do squat for them.
"I have something to say! It's better to burn out then to fade away!"
Paladiamors is correct in that, IO set bonuses only affect you. IO procs will trigger when the pet uses a power that uses that enhancement type.
Hey - if I slot in an IO set bonus that gives (for example) +2.0% damage, will my pets be affected by that damage increase, or is it just abilities that I use directly?
As an aside, if there's a central thread or source of information concerning Mastermind IO slotting specifics, I'd love to see it (and not create redundant threads).
Thanks.