I haven't read anything after this post and I know it was a couple weeks ago, but I remember one baseball analyst once describing health as a skill; in other words, according to that view, the above is a false dichotomy. Health isn't (only) luck or a "blessing," it is something a player can--at least to some degree--develop and cultivate.
Of course I think it is both. Sometimes players are just unlucky or have a problematic body type, or a play style that is more conducive to injury. I don't want to blame Delpo for his woes. But I do think that when you look at someone like Roger, it isn't only or even mainly luck or being blessed. He has been very smart about his body, and he has developed the ability to stay healthy like a skill.
In other words, I don't think it is all that accurate to say that Rafa has been less lucky than Roger. Maybe that is partially true, but it could also be said that Roger has been better at staying healthy.