Kidd does kind of seem like he fulfills Shiki role. Sorta? I'm not sure.
I don't see Law as anything like WB, however. WB was Roger's biggest rival (not enemy, but rival). WB/Roger is a situation akin to Mihawk/Shanks, if anything. Law does not have that kind of portrayal with Luffy.
Law is his own character, I don't see Law representing any of the older generation there. WB's relationship with Roger is very little to nothing like Law. Law is far, far more of an ally than rival anyway, no matter how much he tries to insist otherwise- and those gags of him "following" Luffy's orders, etc, exist to just banter at that a little.
Not saying Law can't be uber strong or whatever, just don't see any correlation. There's no reference, no parallel, nada.