I think Bludgeon would make a better Samurai. Out of the TF Prime toys, I'd stay with Wheeljack -- he's already very Drift^Samurai-like as it is.

Tetchan: I think this Optimus Prime wouldn't be a good ninja because:
#1: Optimus Prime is all noble and honourable and crap... ninjas sneak around in shadows and stab you in the back.
#2: Aside from being red, he has those very bright light piping blues (with an LED light up weapon!). Not very stealthy. This!!