Here's references from two show websites:
The sickle feathers must be equal in length and they must extend approximately one inch above the rest of the tail,and should be stiff and held straight in an upright position. Soft flopping sickles are faulty and undesirable. Those which are too long and curl over are also undesirable
Soft, floppy sickles or sickles that are too long and curl over are faulty and
undesirable.
His tail is a defect, not a sign of a cross. I've also seen several Seramas who aren't very vertical, and know several breeders who discourage being vertical because it's not very healthy for their organs.
And his legs are actually yellow, the lighting in the room and the camera flash made them look white.
I don't think he's crossed.
If he is, I traded a perfect SQ pair of Silkies for a pair of mutts. Who knows about the hen? She has no sickles to tell if they'd be curved or not. But from what I've read curved sickles are a common defect.