So first you remove the rear wheel and clean/lube those splines. Then you pull the rear differential and the driveshaft to clean and lube those splines? I've had Moto Guzzis for years and that's what I've always done. But why use different grease on the rear wheel and driveshaft splines?
Short answers:
First question: Yes.
Second question: Because Honda specifies different lubricants for those applications. I'll trust their engineers until I hear compelling reasons to use something else. I've heard reasons, but none compelling enough for me to change products.