Sizewise, yes, he could hurt the silkies. Agressiveness-wise, every cockerel/rooster is different, so while there are breeds that have reputations for being more aggressive (and that's usually referring to how they are with people) it doesn't mean it's a sure thing. I've had really nice roosters of several breeds, and a couple of nasty ones, so you really never know. Time will tell for that. I have found that very friendly, cuddly cockerels often turn out to be the meaner ones. The ones that give you space and stay out of your way tend to be better keepers.
