Not only can he, but most likely he will. The larger the rooster and the smaller the hen, the greater the chance that he can 'make contact'. Where there's a will, there's a way.
I have the same question. Our silkie "hen" just started crowing.... whoops...
He's not aggressive so I thought I would keep him, but now I am concerned about breeding, which is not what we intended to do when we got chickens. We barely have room for the ones we have! I think I have to post in a whole other forum or two just to learn about fertilized eggs vs. non fert. and broody hens and finding homes for chicks and things like that. Luckily I've got a little time. Our chickens are about 5 months old.
That being said, I would love to seem some pictures of the mixes that occur...