If I remember correctly, silkies where used way back during the creation of the breed and the silkie traits still come throught today. From the 8 silkies I hatched from bought eggs, one of the pullets was silkie feathered, but she was killed by a cat.
As for the cross, I know my young serama roo was chasing the silkie hens yesterday, but he didn't catch any that I saw, the silkie hens are young POL pullets too, so they weren't willing to let him. But I would imagine it would be very possible for fertilization to occurr if the roo is successful in mounting the hen and she cooperates. I believe the cross should produce smooth feathered (maybe some silke feathered) birds with feathered feet and little crests.