I just would like to mention that I may be making more of the riddle than is actually there. It may simply express the idea that "the other world" is some sort of mirror world that one "crosses" into upon leaving this one. 

So, if the W in Wye is not part of the puzzle, then the riddle becomes a simple palindrome:

"ZestY SKaters crossed at eXe and wYe" or "Z Y SK:X Y Z."

As Mr Lipon notes the "special frost" may simply mean an extra-hard frost that would make crossing possible at fast-flowing the "neck". 

On the other hand, a reference to Lochinvar, who arrived late at his own wedding and ended up Hades-like abducting his bride may be lurking in the lochan. So might Shade somehow be Hades after all? I have long suspected Shade had more than a little to do with Hazel's death (Hazel's shade). 

Haven't you & Tiffany discussed something approaching this, Matt?

NY Lora C